open faces of the four clips 121 are presented to one axial end of the assembly and between the limbs of each clip is slidably disposed a square crosshead 122 having a central bore 123 the four bores 123 are thus parallel to the rotational axis of the rotor 113 the inner ends of the bores 114 communicate with recesses 116 in the hub assembly the recesses 116 being defined by apertures in a sleeve 141 rotatably disposed on a fixed shaft 111 extending through the shaft 111 with its axis parallel to but spaced from the axis of the shaft 111 is a spindle 125 having a stub axle 126 projecting from its one end the axis of the stub axle 126 is parallel to but spaced from the axis of the spindle 125 a lever 127 is connected to the spindle 125 and facilitates rotation of the spindle 125 within the shaft 111 a connecting link 120 connects the lever 127 to the sleeve 141 so that the spindle 125 and sleeve 141 rotates as one relative to the shaft 111 the stub axle 126 is rotatably received in a bush 129 of a plate 128 the plate 128 forms part of the stroke member of the pump and carries four axially extending equi angularly spaced posts 131 each.