Biology Puzzle

I worked in a home improvement store and had a biology teacher ask me for help one day. She was trying to find hands on models of he different types of joints in the human body and was on a really limited budget. There a three types of joints, ball and socket, sliding, and hinged. The hinged one was easy. We simply found some clearanced hinges for about 50 cents each. Next on the agenda was the ball and socket joint. We eventually came up with grease fittings stuck inside the tip of a piece of rubber tubing. The hardest one is the sliding joint (wrist) which we found was best demonstrated by a sliding lid support hinge. I was able to come up with ten sets of "joints" for her classroom for about $25. Never thought I would need my biology classes working in home improvement stores!!!!!