What is "caulkin"

A caulkin (or caulk; US spelling "calkin" or "calk") from the Latin calx (the heel) is a blunt projection on a horseshoe that is often forged, welded or brazed onto the shoe. The term may also refer to traction devices screwed into the bottom of a horseshoe, also commonly called shoe studs or screw-in calks. These are usually a blunt spiked cleat, usually placed at the sides of the shoe.