There were three versions of Starrett’s spring-type calipers and dividers, the “Fay”, the “Yankee” and the Toolmakers’. They still make the “Yankee” and the Toolmakers’, albeit in a more limited range of sizes than was once the case.
The calipers and dividers you show as 001, 002 and 003 are of the “Yankee” pattern. The outside caliper (004) is of the Toolmakers’ pattern, note that its legs are of round cross-section compared to the “Yankee” pattern being made from flat stock. In general over the years Starrett has simplified how they mark their tools so “The L.S. Starrett Co.” would predate “Starrett” on your particular tools. I don’t have dates for when these changes were made. I have a Toolmakers’ inside caliper I bought new in the late 1970’s that’s marked “The L.S. Starrett Co. Athol Mass U.S.A.” and a Toolmakers’ outside caliper bought new early this year that is marked simply “Starrett”; this marking looks quite like what you show on your Toolmakers’ caliper.
Your “Yankee” pattern instruments show solid adjusting nuts with what I call a “ropish” knurl (not sure it qualifies as a true “rope” knurl). At some point Starrett changed this to a diamond knurl. My Starrett catalogue 29, copyright 1993 shows a diamond knurl on the solid nut for these while the 3rd ed., catalogue 28, also copyright 1993, shows a “ropish” knurl. My caveat here is that this edition of catalogue 28 looks like it’s still using the illustrations that are in catalogue 27 so at least some of the illustrations in it may have been out of date by 1993 (are we all following this?)
Per an article by E.F. Markham in “American Machinist”, October 2, 1902 (retrieved on line): Charles Fay designed the “Fay” and then the “Yankee” pattern calipers and dividers in the mid 1880’s, the "Yankee" pattern costing less. The "Fay" pattern instruments were made by starting with square stock so required more forming. In particular Fay patented the now familiar arrangement of a partially circular spring holding the two legs with notches securely to a fulcrum pin. BUT if you look at the original patent drawing (patent no. 319,215), instead of both legs being notched with a separate fulcrum pin, one leg is notched and the fulcrum as it were is formed as a projection on the inside of the opposite leg. Probably didn’t take long to realize that notching both legs and using a separate fulcrum pin was an improvement. In 1887 Fay went to work for Starrett to supervise the production of the “Fay” and “Yankee” line there.
From Kenneth Cope’s Makers of American Machinist’s Tools, Astragal Press, 1994, it looks like the Toolmakers’ pattern of calipers and dividers came out in 1909.
David
