Abstract: A shaft 44, 144, 145 is conventionally driveably connected to a bore 46, 146 by a steel key of rectangular cross-section. Where the shaft is of smaller diameter than the bore, a slotted nylon sleeve is fitted between them and a tall steel key extends through the slot. Failure of both standard and tall keys can occur for various reasons. A unitary component 50, 162, 163 of suitable plastics material or non-ferrous metal is therefore proposed. This component essentially includes an integral key 56, 174 of curved cross-section adapted to engage in a mating keyway 176 formed in the bore. Where the shaft 44 and bore 46 are nominally of the same diameter, the component 50 consists also of an integral key 52 of rectangular cross-section adapted to engage in the conventional keyway 48 in the shaft.