Ring and ball, mounted on separate handle ball.
An apparatus for demonstrating thermal expansion, comprising a captive brass ball secured to a mounted brass ring by a chin, Ring mounted on rod with a wooden handle. The brass ball will pass through the ring when both ball and ring are the same temperature (i.e., both hot or cold). However, if you heat the ball but not the ring, the ball cannot pass through! Both ball and ring are mounted on wooden handles and are approximately 1" in diameter.