One of many in the Cast Puzzle series, Hanayama Co. 2007.
(metal, outside diameter 1.8 inches, inside diameter 1.1 inches;
the beveled ends of the two pieces have magnets in them)

The straightforward way to assemble the two pieces is to start with the two ends touching and twist counter clockwise. However this ends with the two beveled ends meeting backwards:



Instead, start with the inside ends of the two pieces meeting and twist clockwise, and the two bevels will meet properly to allow the magnets to snap the ring in place: