Purchased circa 1995.
(aluminum, 3.75 inches)
This puzzle at first appears to be made of two pieces, the post and the turret, that can wiggle a bit but won't come apart. However, the surface inside the turret can be pushed down against a spring. By holding the puzzle upside-down, and pushing in, the surface can spin until a brass pin inside can drop down and allow the turret to be unscrewed. Inside is a pawn: