Reamble Idham couplings are somewhat dated, but flexible coupling design, consisting of identical left- and right-hand hubs th dogs that sandwich a spacer between them. The coupling was originally developed to address aft misalignment on a ddlewheel steamer. Unlike many uplings, the Oldham coupling sign is specifically intended for machines whose shafts have parallel misalignment, as opposed angular and axial misalignment. ial misalignment is when two aft ends should meet but do not is is also called an end float in ce the shafts float without connecting). Typically, axial misalignment should not exceed 10% of the major diameter the spacer. motion control applications, the spacer is often manufactured from a polymer such nylon or acetal or a combination thereof. To minimize backlash, the spacer disused into the mating slotted halves, which are often constructed from aluminum to imize inertia (or brass, in smaller sizes). Because of the sliding friction that develops, ar of the spacer will eventually introduce backlash