Swivel Head Screws use our patented left-hand-thread swivel-foot system. The ball end of the body screws into the foot for easy installation and removal. Once the ball threads pass beyond the foot threads, the foot can rotate and pivot freely (20° total angle). Foot threads are left-hand to positively prevent accidental backout during use. Delrin® feet are optional for types A and B. Note: Delrin® feet are not threaded – they snap on and off.