Alloy Artifacts

Socket Identification

Logo from a Duro Socket Set, ca. 1929-1930.

The early sockets produced by Duro and Indestro are frequently difficult to identify, as they were typically marked only with the size and possibly an obscure symbol. In some cases, the only guide to the maker is the overall design and construction of the socket, and this too may be ambiguous; other manufacturers' early sockets were made in a similar manner.

In this section we'll look at a number of examples of sockets and socket sets from Duro and Indestro, and develop guidelines and characteristics for identifying the sockets.

Early Hex-Drive Sockets

Sets of hex-drive sockets in metal boxes were offered by a number of manufacturers, at least as early as 1915. It's likely that Duro and Indestro offered these from the early 1920s or before.

Indestro No. 220 Socket Set

Fig. 29 below shows an early hex-drive socket set from Indestro, complete with a steel container with an embossed lid. The fractional sizes are written in the style "5-8" rather than expected "5/8" form; this appears frequently on early sockets, though some socket sets have the syles in mixed format.

Fig. 29. An Early Indestro No. 220 Hex-Drive Socket Set.

Note that the sockets are marked with five-pointed stars on either side of the size markings; this pattern appears on several examples of Indestro sockets, suggesting that this was intended as a specific mark for Indestro. (As a counterargument though, early sockets from Bog Mfg. of Chicago also show similar markings with stars on either side of the size.)

The sockets in this set use 1/2 inch hex drive and are all six-point. The sockets were constructed by machining and cold-broaching, and were then hardened, making them impervious to wear but subject to cracking. The band of knurling is coarse enough that it was likely intended to be functional, to allow the socket to be turned by hand.

Indestro No. 19 Socket Set

Fig. 30 shows another Indestro socket kit, this time with a clever "streamlined" holder resembling a locomotive. The set includes a 1/2-hex drive L-handle marked "Indestro Mfg. Co. Chicago", eight sockets marked with fractional sizes, and a screwdriver bit.

Fig. 30. Indestro No. 19 Socket Kit with Streamlined Holder, ca. 1925.

The sockets have hex (6-point) broachings and a reduced base, and the construction is similar to that in the previous example. A knurled band is provided to assist with hand turning.

This set is not marked with a model number, but a 1925 catalog from United Hardware & Tool Corp. lists this model as a No. 19, and shows two other Indestro socket sets as well. The 1941 Indestro catalog lists an updated version of this set as No. 1219, with 12-point sockets instead of 6-point.

The socket holder is rather complicated, with three separate movable pieces attached to the base. To open, the nose piece first folds forward to release the hex wrench, then the tail piece pivots to the side, and finally the retaining rail lifts up to free the sockets. (The retaining rail even has a slot to engage the tip of the screwdriver bit.) Duro Metal Products developed and patented a number of such socket kits, although this particular one doesn't appear to be patented.

Duro LTX316 Socket Set

We recently acquired a Duro Metal Products LTX316 socket set, a compact set with a driver and sockets in a tapered metal box. The set was manufactured around 1930 and so provides a valuable snapshot of Duro socket production at that time.

Fig. 31. Cover of Duro Metal Products LTX316 Socket Set, ca. 1929-1930.

Fig. 31 at the left shows the top cover from the socket set, a lid that slides into place on the tapered box. The center is stamped with a fancy logo for Duro Metal Products, a design also seen on their valve grinder tools.

The stamped "LTX" and "316" markings are presumed to identify the model number for this set, but currently no catalog reference is known for this model.

Fig. 32 shows the Duro Metal Products LTX316 socket set, consisting of a convertible L-T handle with 12 hex sockets and three square sockets. The set is contained in a tapered metal case with a sliding cover, a popular means of storage for socket sets of this type.

Fig. 32. Duro Metal Products LTX316 1/2-Hex Drive Socket Set, ca. 1929-1930.

The driver and sockets all use 1/2-hex drive, and the generous assortment of sockets includes hex sizes 5/16, 11/32, 3/8, 7/16, 1/2, 9/16, 19/32, 5/8, 11/16, 3/4, 25/32, and 7/8. The three square sockets have sizes 5/16, 11/32, and 3/8.

The L-T handle is a convertible design and has been noted previously in our section on Duro patents; the corresponding patent is #1,744,413, issued in 1930. This particular example is marked "Duro Metal Products Co." and "Chicago U.S.A.", with a "Pat. Pend." notation at the left. Based on the patent filing date, the pending status indicates a manufacturing date of 1929-1930. The bright finish appears to be nickel plating.

A later example of this tool, taken from a very similar socket set, can be seen as the L-T Handle Patent.

L-T Handle in Open Position

Fig. 33. Duro 1/2-Hex Drive L-T Handle Showing Open Position, ca. 1929-1930.

The L-T handle was normally stored with the L-handle inserted into the sheath, as shown in the figure above, and it could be used as an L-handle in this form if desired.

If operation as a T-handle was required, the handle was first removed, then the short arm inserted into the sheath. The arm locks into place against a stamped dimple in the sheath. Fig. 33 at the left shows the L-T handle as it appears when assembled as a T-handle.

Most of the sockets in the LTX316 set are marked only with the fractional size, but several of them also have a distinctive trapezoid symbol marked on each side of the size. Fig. 34 shows two of the marked sockets, both with hex broachings and sizes 3/8 and 7/16. (Note that the opening shown in the photograph is the 1/2-hex drive end.)

Fig. 34. Duro 1/2-Hex Drive Sockets, ca. 1929-1930.

The trapezoid symbol resembles a stylized "D", and has been identified in a catalog as a mark for Duro production. Additional examples will be shown later with the Duro 1/2-Drive Sockets.

The sockets have been machined from bar stock, cold-broached, and then hardened, the standard construction method at the time. The decorative band of cross-hatching appears around the top of the larger sockets, but around the base of the smaller sockets shown in the figure, as these have been inverted to simplify the manufacturing. The finish is cadmium plating.

To place this socket set in context, the LTX316 set appears to be virtually the same as a socket set listed in the Sears Roebuck 1929-1930 Fall and Winter catalog. The Sears set is listed as the "Merit Tool" 16-Piece Socket Wrench Set, and the description mentions the L-T handle, 15 sockets ranging from 5/16 to 7/8, and the metal case with a sliding lid. There are a few minor differences -- the metal case is green, and the tool finish is described as white nickel -- but these changes could be easily made during manufacturing. (The listing is on page 1122, for any readers with a copy of this catalog.)

The "Merit Tool" brand appears to have been a generic name used by Sears for whatever tools had been selected by their buyers, and may or may not have been actually marked on the tools. One of the advantages of the metal container used for this set is that the cover could be easily stamped with whatever brand the customer wanted. The price for the "Merit Tool" set was just $0.95.

Early Square-Drive Sockets

The 1/2 square drive size had emerged as a standard even before 1920, and was preferred for more demanding socket wrench applications. The early makers of these tools included Blackhawk, Snap-On, and Walden, and it's likely that Duro and Indestro had joined the group by the early to mid 1920s.

Indestro Square-Drive Sockets

Fig. 35 below shows three early 1/2 square-drive sockets from an Indestro set. Note that the markings include five-pointed stars on either side of the size, a feature noted in the earlier No. 220 Socket Set as well as on the Indestro Socket Wrench shown elsewhere in this article. The production date of this set is unknown, but likely dates from the mid to late 1920s.

Fig. 35. Early Indestro 1/2 Sq. Drive 6-Point Sockets.

The construction of these sockets is similar to those in the No. 220 set. The sockets were first machined, then cold-broached for the six-point hex opening, and finally hardened; they also appear to be finished with a thin bright plating.

Fig. 36. Broaching Detail for Early 1/2-Drive Indestro Sockets.

Fig. 36 at the left shows a closeup of the socket construction. If you look carefully at the upper righthand socket, you can see a small burr left by the broaching, showing that the broaching came after the recess was machined. The centers of the flats also show tooling marks where the socket was drilled out prior to broaching.

Duro Square-Drive Sockets

Fig. 37 below shows several sockets believed to be examples of early Duro production. These are from a socket set that included a Duro Metal 672 ratchet marked "Patent Pending"; assuming that the ratchet is the original one for the set, this would imply production around 1928-1931.

Fig. 37. Early Duro 1/2 Sq. Drive 6-Point Sockets.

The sockets in this set are very similar in construction to those in the early Indestro set discussed above, but are marked with an odd trapezoidal symbol on either side of the size, where the Indestro sockets used a five-pointed star.

This trapezoid symbol had been assumed to be an identification mark for Duro, an assumption that was confirmed by a recently acquired 1939 Duro full-size catalog. The catalog (p. 40) shows an illustration of a "Special Carbon Manganese Steel Socket" with the two trapezoid symbols clearly visible on either side of the size marking. (We'll refer to this symbol as the D-Trapezoid Logo for ease of reference.)

Apart from the markings, another difference from the (likely earlier) Indestro sockets is that the knurling on the Duro sockets is now a very fine cross-hatch, giving them a more refined appearance. The coarse knurling on early sockets was probably intended as a functional feature, to allow the socket to be turned easily by hand, but later evolved to a more decorative role.

Although these sockets are marked only with the D-Trapezoid and size, the 1939 catalog shows the model numbers that were used for the series. The numbers have the form "99xx" where "xx" is the size in 32nds, so for example model 9924 indicates a 3/4 size. The square and double-square broachings are identified with an appended "S", e.g. model 9920S for the 5/8 size.

Durobilt Socket Set

The 1931 Sears Roebuck Spring and Summer catalog devotes half a page to "Durobilt" brand socket sets, and the tools in the illustrations closely resemble the known Duro and Indestro socket sets. Although these Durobilt sets are now quite rare, we recently were able to acquire one, and can now confirm that Duro Metal Products was the manufacturer. The socket set is currently being prepared for display, but we'll offer some photographs and observations in advance.

Fig. 38. Durobilt Decal from 1/2-Drive Durobilt Socket Set.

The set we acquired is listed in the catalog as the "36-Piece Wrench Set", and consists of drive tools and sockets in a hinged metal case. (The set is on page 483, for any readers with this Sears catalog.) A check of the contents with the catalog listing showed that our set is nearly complete, with only a few pieces missing.

The inside lid of the case has a Durobilt decal, as shown in Fig. 38 at the left. The decal matches the one shown in the Sears catalog, so the identification of the set is quite certain.

Fig. 39. Duro Durobilt 1/2-Drive Socket Set, ca. 1930-1931.

Fig. 39 shows the Durobilt 1/2-drive socket set as acquired, but with two missing tools filled in from our general inventory.

The ratchet handle in the set is the Duro 672 model discussed in a prior section, and the ratchet is marked with a patent pending notation. The patent status together with the known catalog reference places the manufacturing date right around 1930-1931, and this will prove very helpful in providing a time context for other Duro tools.

The rare set was quite a significant find, as this is currently our earliest known example of 1/2-drive socket tools sold by Sears Roebuck. (Or at least the earliest example for which a reasonable estimate of manufacturing date can be made.)

The 1930-1931 origin of this set predates the Craftsman C-Series tools by a year or two, and predates the familiar Craftsman "BE" Series by three years or so.

Early 12-point Sockets

During most of the 1920s sockets were generally made with six-point (or four-point) broaching, but by the late 1920s and early 1930s companies were starting to produce 12-point sockets. Duro/Indestro also began producing 12-point sockets in this time frame; although the earliest date is not known, we do know that by 1931 Duro and Indestro socket sets were definitely available in 12-point broachings.

The first confirmation comes from the 1931 Sears catalog, which lists several "Durobilt" brand socket sets that are easily recognizable as Duro production. The high-end set featured chrome-nickel sockets in the standard 6-point broaching, but with 12-point sockets available at a slightly higher price.

A second confirmation is even more direct: by fortunate circumstance we were able to acquire a rare early Indestro Chromium-Vanadium 12-point socket set, with an even more rare dated sales receipt. The set consists of ten 12-point sockets, a speeder, T-slider, ratchet adapter, extensions, and a universal, with most of the pieces being marked "Chromium-Vanadium". The speeder was also marked "Indestro Chicago", and the metal box has an Indestro decal on the top, similar to the Indestro Logo shown below.

The sales receipt shows that the set was purchased on August 8, 1931 from a Western Auto store in Texas, for a price of $5.35. As additional verification, a 1932 Western Auto catalog does indeed offer a Chromium-Vanadium socket set matching the above description, and for the same $5.35 price.

Indestro 1/2-Drive Chromium-Vanadium Socket Set

With the above introduction, Fig. 40 shows the Indestro Chromium-Vanadium socket set from 1931. The ten sockets are marked "Chromium-Vanadium" except for one, and all of the drive tools are similarly marked, except for the unmarked universal and double-male extension.

Fig. 40. Indestro 1/2-Drive Chromium-Vanadium 12-Point Socket Set, 1931.

Photographs of the individual tools were shown in a prior section and won't be repeated here, but these links will show the Speeder, T-Slider Breaker Bar, Extension and Universal, and Ratchet Adapter.

Fig. 41 shows nine of the sockets from the set; the smallest (7/16) socket didn't match the others, and appears to be a replacement. All of the sockets shown are marked "Chromium-Vanadium" and have a star symbol on each side of the size, a characteristic marking for Indestro sockets.

Fig. 41. Indestro 1/2-Drive Chromium-Vanadium 12-Point Sockets, with Inset for Detail, 1931.

The sizes are, from the front left, 1/2, 9/16, 5/8, 21/32, and 11/16; and in the back row, 3/4, 13/16, 7/8, and 15/16. The inset shows a typical "Chromium-Vanadium" marking.

The sockets have a coarse knurled band around the base, probably intended to help with turning a loose nut by hand.

The socket construction is cold-broached with a bored recess at the base. If you look carefully at the full-sized photograph, you can see chatter marks typically left by cold broaching.

Duro No. 500 Socket Set

As 12-point broachings became standard for alloy steel sockets, Duro/Indestro changed its carbon steel (or "Select Steel") economy socket sets to 12-points as well. Although the dates are uncertain, the two examples below are thought to be representative of Duro and Indestro economy-line 12-point sockets in the early 1930s.

Fig. 42. Duro 500 Handle with Early Hex-Drive 12-Point Sockets.

Fig. 42 at the left shows a partial No. 500 set consisting of a Duro 500 hex-drive handle and several sockets. The handle is marked "Duro Metal Products Co." and "Chicago U.S.A", along with a notice for patent #1,788,535, issued in 1931.

The full No. 500 set included the L-handle, a ratchet, eight sockets, and screwdriver bit, all contained in a distinctive fold-open metal case. (The metal case is the subject of the patent mentioned.) We recently acquired complete set of somewhat later origin, and will add a photograph in the near future.

We currently have two catalog references for the No. 500 set, the first of which is the 1933 Ducommun Catalog "H". This catalog illustrates the No. 500 set, as above but with hex sockets, and also shows a No. 500XX set with 12-point sockets. The price listed was $2.00 for No. 500 and $2.25 for NO. 500XX.

The second reference is the 1939 Duro catalog, which lists the Duro No. 500 socket set with contents as above.

Indestro No. 1236 1/2-Hex Drive Socket Set

Fig. 43. Indestro No. 1236 1/2-Hex Drive Socket Kit with Ratchet, Handle, and Folding Holder.

Fig. 43 shows a mostly complete Indestro No. 1236 socket set consisting of a ratchet, a hex handle, a screwdriver bit (doing double-duty as the ratchet plug), and the 12-point sockets, all wrapped up with one of the clever holders that were an Indestro specialty. No model number is marked, but the set is similar to the No. 1236 set shown in the 1941 Indestro catalog, with a few sockets missing.

Of the pieces here, only the ratchet is marked, with "Indestro Mfg. Co. Chicago, U.S.A.". The sockets have been simplified to a plain cylindrical form, although they retain the fine cross-hatching at the base.

Indestro No. 1536 1/2-Drive Socket Set

Fig. 44. Indestro No. 1536 1/2-Drive Socket Set.

Fig. 44 shows an Indestro No. 1536 1/2-drive socket set in a metal case, identified by the illustration of the No. 1536 "36 Piece Master Socket Set" listed on page 31 of the 1937 Indestro catalog.

Based on the list of contents in the 1937 catalog, the set in the Fig. 44 is nearly complete, missing only the short extension (ratchet plug), screwdriver bit, and the valve grinder attachment. (This set also includes one extra double-hex socket.)

This set is an example of the carbon-manganese steel economy grade socket sets sold by Duro and Indestro in the 1930s. The 1937 catalog price for the No. 1536 set was just $6.40, less than half the price of a similar "Super Quality" chrome-vanadium steel set.

The empty corral in the upper left corner of the case was for six drain plug sockets, apparently an optional item for the early versions of this set. By 1937 the illustration showed the small corral holding some of the smaller hex sockets, with the main corral having been reduced in size.

Fig. 45. Indestro Logo from No. 1536 Socket Set.

The Indestro decal on the lid of the case is shown in Fig. 45, although unfortunately it's a bit difficult to read due to the glare from the finish. This decal is identical to the decal on an earlier socket set, examples from which were shown as the Early Indestro Sockets above, so apparently these sets were sold for some period of time.

One additional note regarding this set: of the tools in the set, only the ratchet handle had an identification mark, and that was only the patent number for the ratchet. If the decal with the Indestro logo case were lost or obliterated, or the tools dispersed from the case, it would be difficult to identify them as part of an Indestro set.

Although the sockets in this set are marked only with the size, the Indestro catalogs did assign model numbers to the series, similar to the numbering used for the Duro D-Trapezoid sockets described above. The 1937 Indestro catalog (p. 26) shows these sockets in a table "Master Sockets", with model numbers of the form 66xx where xx is the size in 32nds, e.g. 6624 for the 3/4 size. Similar to the case for Duro, the square and double-square sockets have a "-S" appended, e.g. 6624-S.

While we're mentioning the Indestro 1937 catalog, it's worth noting a statement from the catalog that may prove significant for a later discussion. In referring to the "Selected Steel Sockets", the catalog states: "The Sockets are accurately broached and the heat treating, tempering, and hardening is done under our own supervision, in our own factory ...". Note that the careful wording doesn't say that Indestro actually machined the socket blanks.

The older Select Steel (Carbon-Manganese) socket sets included drain plug sockets with sizes ranging from 5/16 to 11/16, with corresponding model numbers 9951-9957 for Duro and 6651-6657 for Indestro. Fig. 46 shows an example of the Duro 9954 socket, marked with the size (1/2) and the D-Trapezoid symbol. The corresponding Indestro pieces are essentially identical, except that they omit the D-Trapezoid marking.

Fig. 46. Select Steel 1/2 Inch Drain Plug Socket with D-Trapezoid Symbol, Duro Catalog Model 9954.

Fig. 47. Chromium Vanadium 1/2 Inch Drain Plug Socket, Indestro Catalog Model 3316.

The newer alloy steel socket sets also included drain plug sockets. Duro offered these in sizes from 5/16 to 3/4 by 16ths, plus the 11/32 and 13/32 (hexagon) sizes for Hudson-Essex applications. The model numbers were of the form "13xx" where "xx" is the size in 32nds.

Indestro offered fewer sizes, just 5/16, 3/8, 7/16, and 1/2 with model numbers of the form "33xx" as above. Fig. 47 at the left shows an example, an Indestro 3316 1/2 inch drain plug socket marked "Chromium Vanadium".

The Development of Hot-Broached Sockets

In May of 1935 Duro filed for an important patent on their new hot-broaching method for making sockets, and the patent was issued as #2,027,922 in January, 1936. The patent document has an excellent discussion of the prior art (cold-broaching) and the advantages of hot-broaching, and is highly recommended for anyone interested in the how and why of such things. Among the advantages cited are the increased strength of the sockets, the smooth broach free of chatter marks, and the relieved lip at the drive end that allows for easier connection to a drive tool. (The patent even mentions the attractive "scalloped" appearance of the metal pushed ahead of the broach.)

Early Duro-Chrome 16xx-Series Sockets

Fig. 48. Early Duro-Chrome 1/2-Drive Hot-Broached Sockets, with Inset for Broaching, ca. 1935-1937.

Fig. 48 shows several early Duro-Chrome hot-broached sockets in the 1/2-drive 16xx series, with an inset at the top to illustrate the broaching details. The sockets are marked "Duro-Chrome" and have a cross-hatched band flush with the surface.

The models and sizes are, from the left, 1628 (7/8), 1630 (15/16), 1632 (1 In.), and 1634 (1-1/16).

A close look at the inset shows some degree of variation in the shelf left by the broaching; in particular, the rightmost socket has a wide shelf with nearly perpendicular scallops. This suggests that Duro was still experimenting with their process at this early stage. The third socket from the left (model 1632) most closely resembles the modern form.

The drive openings of these sockets have smooth walls without the recesses found on modern sockets, another indication of their early manufacturing date.

By fortunate circumstance, it turns out that the hot-broach patent helps to estimate the production date of the Indestro Chromium-Vanadium Socket Set displayed on a previous page. On close inspection of the sockets in that set, it turned out that some were hot-broached, while others were of the older cold-broached construction. With the reasonable assumption that production would have quickly shifted to the new hot process, this suggests that the Chromium-Vanadium socket set was probably made in the 1935-1936 time frame. The socket set thus gives us a valuable snapshot of the design and construction of sockets being produced at that time.

In particular, we see that the sockets have the tapered walls and knurled base of the later modern sockets, and that the sockets were being finished with a highly polished chrome plating. Part numbers were not yet being used at this time, though, as the sockets have only the size markings.

Modern Sockets

Duro and Indestro must have been very busy during the late 1930s, as their socket lineup developed very rapidly in these years. By the time of the 1938 Duro-Chrome catalog (38M), almost all of the modern series of sockets had been developed, and the sockets had been assigned part numbers. These included the 1/2-drive 11xx, 16xxx, 12xx, and 14xx (deep) series sockets, the 3/8-drive 44xx series, and the 1/4-drive 45xx series.

Fig. 49. Duro-Chrome 1/2 Drive Sockets, Left to Right: 1118, 1618V8XY, 1625, 1622S.

Fig. 49 at the left shows the top-of-the-line for 1/2-drive sockets, the 11xx series with thin straight walls and 16xx series for thin tapered walls. These included selected 8-point sizes (marked by appending an "S" to the model number) and the specialty 1618V8XY socket, the latter made with ultra-thin walls for certain connecting-rod bolts.

The models and sizes are, from the left, 1118 (9/16), 1618VbXY (9/16), 1625 (25/32), and 1622S (11/16, 8-Point).

12xx-Series Chrome-Vanadium Sockets

The 1938 Duro catalog also shows a 12xx series of 1/2 drive 12-point (and 8-point) sockets that it refers to as "Chrome Vanadium sockets"; these are the model numbers that would later become the Indestro Super line. At this time they were marked with "Chromium-Vanadium" and the model number, as shown in Fig. 50 below.

Fig. 50. Duro Chromium-Vanadium Sockets, Left to Right: 2812, 1220S, 1234.

The socket on the right, marked 1234 (size 1-1/16 inch) is believed to date to the '30s, as it shows the cross-hatching in use at this time. Later on these models changed to the simpler straight knurling shown on the middle and left sockets. The 1220S number on the middle socket indicates an 8-point broaching.

The leftmost socket is a 1/4-drive 3/8 socket and has model number 2812; although this model is not shown in the 1938 catalog, a later Indestro catalog lists 2812 as one of the Indestro Super 1/4 drive line. This again confirms the continuity of the "Chromium-Vanadium" mark with the later Indestro Super line, with a likely "Super-Quality" intermediate.

44xx 3/8-Drive Sockets

The 1938 Duro catalog lists the 44xx series of Duro-Chrome 3/8-drive sockets, but for some reason this drive size was not yet available in the tapered thin-wall format offered in 1/2- and 1/4-drive. Instead, the catalog illustration shows these sockets as having narrowed bases and straight walls. An example of this can be seen in the leftmost socket of Fig. 51, marked as Duro-Chrome 4420 with size 5/8.

Fig. 51. Duro-Chrome 3/8 Drive Sockets, Left to Right: 4420, 4414, 4422.

The tapered-wall format was made available later, as the middle and righthand sockets in the figure show. These sockets, marked 4414 7/16 and 4422 11/16 respectively, both show the same fine cross-hatching that was used for the 1/2-drive 11xx and 16xx series (see Fig. 49 above.)

The middle socket shows two other interesting details: the socket is in unfinished steel rather than polished chrome, and it has a small "G" next to the model number. I have one or two other Duro pieces that also show a "G" marking paired with unfinished steel, and this certainly suggests that the "G" may indicate a 1945 production date when government wartime rationing was in effect, as with the "G" date code for Snap-On tools.

Duro-Chrome also offered 1/4-drive sockets in the 45xx series, with tapered walls and a cross-hatched band, but these are not illustrated at this time.

The D-I Sockets: Wartime Production?

There is one other group of sockets that may be seen occasionally, but which don't fit any of the markings previously noted above. These sockets closely resemble the Chromium-Vanadium or Indestro Super sockets, with knurled bases and tapered walls, but are labeled with "D - I" instead of the expected Indestro brand.

Fig. 52. Sockets Marked "D - I" with 12xx Part Numbers.

Fig. 52 at the left gives some examples of D-I sockets; many other examples are available, in drive sizes from 1/4- up to 3/4-drive.

Based on the close physical resemblance of the sockets, the "D - I" notation almost certainly denotes "Duro-Indestro"; in one case I received a set of D-I sockets in a metal box with a Duro-Chrome sticker. In addition, the 1/2-drive D-I sockets usually have a 12xx part number (as in the figure above), offering further evidence of the Duro/Indestro connection. But why would they have been marked differently?

My first assumption was that these might be very early sockets, produced before the standard markings were developed. This fit nicely with the observation that all D-I sockets found to date are either of unfinished steel or have a thin cadmium plating, rather than the polished chrome in use after the mid 1930s.

However, subsequent findings forced rejection of this idea. One piece of contrary evidence is that all D-I sockets found have been hot-broached, which based on the patent date pushes the production to post-1935. Also, the presence of the 12xx part numbers implies production in the late '30s, at which time the standardized marking and polished chrome finishes would be expected.

Another possible explanation is that the D-I sockets were intended as an economy brand, made with cheaper steel and finishes. But if this were the case, they would have been given new part numbers; reusing the 12xx part numbers would be too confusing to customers.

After the above considerations, one explanation remains that appears to fit all of the observations: the D-I sockets represent wartime production, when rationing of key materials (including chromium) forced companies to work with lesser quality steel, or at least forego polished chrome finishes. The D-I sockets might have been produced under a special contracts, as with the Plomb "Wright Field" WF-xxx series tools, or they might have been regular civilian production made to lower standards or with a plain finish. In either event, it would have been desirable to mark the items distinctly so that they wouldn't affect the reputation of the well-known Duro/Indestro brands.

Indestro "Super Quality" 1/4-Drive Socket Set

For one more look at the D-I sockets, Fig. 53 shows a recently acquired 1/4-drive Indestro "Super-Quality" socket set, in which all of the sockets (except one) are marked D-I. (The exception is actually marked "4511 Duro-Chrome", a standard model number for a 1/4-drive 11/32 socket.)

Fig. 53. Indestro "Super Quality" Socket Set with "D - I" Sockets.

Note that the Indestro logo sticker includes "Chrome Vanadium Steel", suggesting that at least for these tools, the steel quality remains uncompromised. Otherwise, the tools have a dull industrial finish and the box is a drab olive color, which would be consistent with wartime production.

Post-Modern Sockets

Sometime in the late 1950s or early 1960s Duro began making changes to their socket designs, with the result that some of the finer features of the earlier sockets were lost. Perhaps this was driven by a need to reduce costs under competitive pressures, but in any event I thought it would be interesting to illustrate the changes.

Fig. 54. Duro Sockets Showing Progressive Changes, from Left: 1619, 1618, 1626, 1634/1234.

Fig. 54 shows a progession of socket design changes, starting from the reference socket on the left, a Duro-Chrome 1619 with tapered walls and a finely cross-hatched knurled band.

The second socket is a Duro-Chrome 1618 and still has tapered walls, but the fine cross-hatching has been replaced with a simpler straight knurled band. The illustrations in Catalog 37-M from around 1961 show that this change had been made by this time.

The third socket from the left is marked as a Duro-Chrome 1626, but now has straight walls instead of the taper, thereby losing what had long been touted as an important feature for working in tight places.

The final change is shown in the rightmost socket, which similarly has straight walls, but is now dual-marked as both a Duro-Chrome 1634 and a Duro-Indestro 1234.

That completes our discussion of Duro/Indestro socket identification. The next sections will present examples of Duro and Indestro tool production, including information on their early tools, the development of alloy steel tools, drive tools and sockets, and specialty tools.