These parts were salvaged from a special mechanical calibration rig. I don't see anything that looks like that in McMaster-Carr, but perhaps I don't know where to look.
The aluminum part is probably custom but the rod (300-series stainless steel) and the plastic (acetal, I think) threaded part with the brass handle look like standard parts. The aluminum part has an internal thread so the depth of the plastic part can be adjusted by screwing it in or out. The plastic part has a conical lead-in and a bore that fits the stainless steel rod with some play. I believe it acted as a pivot with springs to take out the play.