I purchased these as part of a machine shop lot. The person selling the lot did not know what these were. It looks like the half moon slides up on the 2 posts and is locked down by the screw. Other than from the end view, the half moon has an extremely tight fit - lines are not easily visible. There are 4 sizes. The tools are labeled 620-92-04-01 to 620-92-04-04. There is no manufacturer markings. Any idea what they are? Thanks!