the present invention a pin fastener is provided whereby a single embodiment provides high resistance to both shear and tension forces and has a minimum total length and hence weight referring to fig3 the physical relationship between the pin and the work member countersink and opening in use is shown the work member comprises two metal sheets 30 and 31 which are to be tightly held together by the combination of the pin and collar the head portion is double tapered as explained above the first taper 33 axially adjacent the shank 35 having an angle of approximately 82 degrees and the second taper 34 adjacent the top surface 36 of the head having an angle e of approximately 10 degrees it has been found by the applicants that a countersink angle in work member 30 equal to the head taper angle of the pin will frequently result in material fatigue failures at the countersink site these failures have been found to be due to fatigue from tension stresses produced at the countersink of the work member with respect to fatigue failures in general it is a design goal to have such failures occur ultimately at the interface between the two sheets 30 and 31 by designing all other fatigue failures out the pin and hence the combination will ultimately fail at the interface location and the structural effect of the opening in the work.