King Pin Trailer The king pin is a component of the coupling between the semi-trailer and the tractor unit. Different designs make it possible to install king pins onto a trailer quite easily. Ecg Autoparts king pins satisfy the most stringent safety requirements. They are produced from high-quality, coated, forged blanks which are tested for the complete absence of cracks. Exchanging or converting our king pins is both quick and easy. The king pins can be replaced or converted quickly and easily. Ecg Autoparts manufacture King Pin for Trailers 2" & 3.5" for JOST Mechanism. Best Quality EN19 Material used equivalent to SAE5140 and exported worldwide. -Welded on type 2' -Bolted on type 2'/ 3-1/2' -Bolted on type w/ plate and blolt size 2'/ 3-1/2' -Interchangeable with York and jost original