Over the years, keymakers have used virtually every type of bearing between moving parts in keys
and paddles. The bearing, as the intersection of moving parts, can play a big role in the feel of a key and its reliability. Listed below are general types of bearings that have are commonly used in keys and paddles. The type will often include a number of variations. For example, in a "needle and seat" bearing, you might find that the seat is a machined indentation in a larger part, or a an inset separate part made of various metals or even Nylon. Ball and cup bearings are a single ball in a variety of configurations. For the purposes of this survey, assume that you are selecting the best implementation of a particular type.