A kit for use in a procedure for implantation of an orthopaedic joint prosthesis includes a head component of an orthopaedic joint prosthesis, which comprises a body part having a convex bearing surface, and a reverse face at which the head component can be connected to a mating component of the joint prosthesis, in which the head component has a chamfer surface extending around at least part of its periphery where the bearing and reverse faces come together, and a plurality of markings on the chamfer surface. The kit includes a trial head component which comprises a body part having a convex trial bearing surface and a reverse face, in which the trial head component has a plurality of markings on the trial bearing surface at or towards the interface between it and the reverse face. The transverse dimensions of the head component are approximately the same as the transverse dimensions of the trial head component, and in which the location of the markings on the chamfer surface around the periphery of the head component corresponds to the location of the markings on the trial bearing surface of the trial head component around its periphery.