Abstract: A horseshoe stock piece and various complementary pieces provide variety of custom features for horseshoes such as heel calk trailers, trailer calks, calk horseshoes and patent shoes. The stock piece is a horseshoe structure with conventional top or hoof surface, a bottom or ground surface, inner and outer faces, fullering on the ground side, and nail holes within the fullering. The heel end of each arm of the stock piece has a flat, rectangular recess formed in the ground surface face which is from 40%-60% of the depth or thickness of the shoe stock. A transverse groove is formed in the central portion of the recess. The groove has walls which are perpendicular to the surface of the groove and there is a threaded aperture formed in the base of the groove. The foregoing is dimensioned to receive a complementary piece secured in the recess. The complementary piece has a transverse extension or lug extending into the groove.