Yin and Yang Brainteaser Puzzle by Bits and Pieces.  It may take an infinite amount of time to solve this mind-boggling metal brainteaser by designer Doug Engel. Try to take the four nickel-plated pieces apart then fit them back together. 2-1/2" in diameter. Solution included.  Pre-owned in Excellent condition.

“Unlock the brilliance within with this mind-bending puzzle!”