OLDHAM coupler for position switches FGR1, FGR2 and FGR3.
About Oldham couplers:Wikipedia
An Oldham coupling has three discs, one coupled at the inlet, one coupled at the outlet, and a center disc which is joined to the first two by a tongue and groove. The tongue and groove on one side are perpendicular to the tongue and groove on the other. The central disc rotates around its center at the same speed as the input and output shafts. Its center traces a circular orbit, twice per rotation, around the midpoint between the input and output shafts. Often springs are used to reduce play in the mechanism. An advantage of this type of coupling, compared to two universal joints, is its compact size. The coupler is named after John Oldham who invented it in Ireland, in 1821, to solve a problem in the design of a paddle steamer.