Buckling spring

A buckling spring is a type of keyswitch mechanism that was popularized by IBM through its keyboards for the PC, PC/AT, 5250/3270 terminals, PS/2, and other systems. It was used by IBM's Model F keyboards (for instance the AT keyboard), and the more common Model M. It is described in U.S. patent 4,118,611 (Model F) and U.S. patent 4,528,431 (Model M), both now expired. According to the original patent: "A non-teasible, snap action, tactile feedback, key mechanism of extreme mechanical simplicity and high reliability is achieved."