I found these three items that seem to be a set or part of a set, but of what? There are three sizes. The threads are 3/4-16, 7/8-16, and 1 3/16-16. They all have an inverted cone in the threaded end and two flats. They were in a machinist box that had been picked over, but most of the remains were related to machine work. The heavy equipment repair stuff was in the lower roller cabinet, but there was some mixture.