This is a nice, 4" outside spring caliper that is marked "Millers Falls Greenfield Mass." on the steel beam.   It measures 4.5" long overall and has a very nice snug pivot joint, and strong spring. The threaded fine adjustment works great, good threads. It features nice flatten legs, and rounded end tips. A nice looking tool from the 1920's era, perhaps a bit earlier.  No rust, some minor pitting, no damage, minor wear overall, in working order.