Maybe found ancient artifact on a beach in Croatia???

My kids were playing with this in the beach in Croatia, at first thought it was some plastic thing they found. When I picked it up was surprised it was stone.

Basically a hollow rod with machines ridges. Thought it might be part of an ancient tool like a gear or something. One end has a clear notch on the protruding cylinder, other end looks like it may have been broken as there is a ridge although the other surface is very flat.