A compressor for a vehicle air conditioning system comprises a front casing in which is mounted a swash or wobble plate arrangement operatively connected to a drive shaft and a plurality of pistons each provided with a piston body at one end and a foot portion at its other. A cylinder block is also provided defining a plurality of cylinder bores equally distributed circumferentially around the drive shaft, in each of which bores one of the piston bodies can be reciprocated by the swash or wobble plate, as the drive shaft rotates. The inner wall surface of the front casing defines a plurality of longitudinally extending recesses in positions apposed to each piston. The piston body and the foot portion of each piston are connected by a bridge that is bending resistant and projects outwardly into these apposed recesses. Also, at least one side of the bridge is provided with a laterally projecting wing that supports the piston against the adjacent inner wall surface of the front casing to one side of the recess. The front casing and the pistons are thus designed for mutual interengagement and, in the piston, the requirement to provide a bending resistant portion has been divided away from the requirement to provide an anti-rotation locking arrangement.