Hi,
I have seen a very similar thing once and it was identfied by some people as "old/antique grease/lubricant oil nipple" with someone else saying it is some king of tap for liquids. The round hole should in both cases hold another part to be turned to allow liquid /grease to go through.
Google picture search "drip feed oilers " to get an approximate idea
I remain a bit scetical about this since these things are handmade (yours too from the look) and a machine part should be itself machined, shouldnt it?
Greets Namxat