Ah - those are from Niles Bottle Stoppers.They are nicely machined brass inserts that you can epoxy in place to create a threaded connection.
There area some rules - that vary from state to state sometimes, but most insist on a threaded connection or an otherwise provable secure closure for cremation urns.
Truthfully - I do not like the brass inserts. The male portion has a "boss" or thickened portion that protrudes up above the finished surface of the urn. THAT makes you have to adjust the angle of the finial base - and often - that adjusted angle interferes with the aesthetics of the overall lines of the urn with the finial.
Note the dramatic change in direction caused by the steep angle on the base of the traditional type of finial. The next 2 pictures explain why this occurred. The brass insert projecting up above the shoulder of the urn, mandates that you will need to leave enough wood in the finial to cover that. The third picture shows just how deep into the finial you have to cut to accommodate that brass projection. There is not 1/8'' of wood thickness on the finial base - above the brass. So, the only real solution is to trash this finial, and create a more "domed" type as use on the urn for my son'e father in law.