Outside lock joint calipers Starrett (0767)
Info
Large outside compass with fine adjustment screw.
The adjustment screw is conical at the bottom and pushes against a conical dimple on the small leg that is spring loaded. By turning the screw in, the larger leg is pushed farther out. With the big knob, the setting can be fixed.
Inscriptions on leg:
The L.S. Starrett Co.
Athol. Mass. U.S.A.