Abstract: In an internal gear pump comprising a ring gear and a pinion in mesh therewith to define a lunate cavity therebetween, a segmented part-lunate filler inserted in said cavity has supporting faces contacting a pin which extends axially through the cavity and is rotatable about its longitudinal axis. In operation, the resulting forces acting on the filler segments are transmitted to the pin by said supporting faces and produce a torque about the longitudinal pin axis.