A few years back I conducted an extensive research on Lectrolite Corp (LC) and found a lot of info on S-K in the process. The info is scattered in various places on the Vintage forum, but I'll recount what I remember:
--Lectrolite re-designed its 1st tier end wrenches to the now-familiar raised panel style sometime in the late 1940s. These were to become the S-K line of wrenches. They will be marked LECTROLITE and are identical to the later S-K. My main set of SAE end wrenches are 1951 LC.
--In 1952-53, LC established a relationship with S-K with its end wrenches and pliers, which S-K did not manufacture itself (it was focused primarily on socket sets). This relationship continued until 1962-63, when Symington Wayne purchased both S-K and LC, then eliminated the LC brand and absorbed its products/facilities into S-K. These collaboration wrenches bear the mark S-K LECTROLITE. LC stopped marking these raised panel wrenches with its own standalone name, so any RP wrenches with just the LC name are circa 1947-53, and the dual-marked circa 1953-63.
--Under the Wayne ownership, the wrenches are marked S-K WAYNE. Circa 1963-68. For the most part, their mfr is identical to to the LC wrenches.
--Ownership passed to Dresser Industries in 1968, and the wrench markings were changed to S-K TOOLS. It was during this time that they started playing with the finishing and other markings like removing the hatchings from the sockets. QC issues became more of a problem during this period. Although I've never done a case study on which side of the wrench was marked with the brand, I'd suspect this mixing-up would be more prevalent during the DI era. IMPORTANT NOTE: One of the marking changes under DI was the changing of the "C" in the model number from an 'open-C' to a 'closed-C'. This provides another clue to age.
--In 1985, DI sold S-K to Facom Industries. I did not do any extensive research this late because my focus was on the earlier production. I believe it was at this time that the marking was changed to simply "S-K", but could also have happened later in the DI era, I'm just not certain. These can be easily identified as later production by the closed-C.
I believe the "S-dot-K" was introduced by Ideal Industries. Before then, I think it was always S-dash-K. I also think that the full polish S-dash-K were made after management bought the company in 2005. It was after the Ideal buyout that it was changed to S-dot-K, the finishing of the full polish wrenches is noticeably better on the S-dot-K versions.
Hope this helps.
