This is a very nice lock joint inside caliper marked "THE L.S. STARRETT ATHOL MASS. PAT. MAY 21 1895". It is the 6" size, about 6.50" long overall. This caliper is in great shape, with very clean measuring tips, very good pivot joint, and fine adjustment nuts and threads, no rust, or damage, with some discoloration on the bare metal noted. One owner's initial N on one side. A nice clean antique caliper by a well known, quality tool maker!