A joint pin used in scaffolding is a connecting fitting designed to join two scaffold tubes internally, end to end. It is a short steel pin that fits inside the hollow ends of two scaffold tubes. Once inserted, the pin aligns the tubes and allows loads to be transferred through the joint. Joint pins are commonly secured by friction or locking features, depending on the type. Joint pins are mainly used to extend the length of vertical standards in scaffolding. They provide alignment and continuity but are generally not used for high load or critical joints unless specifically designed and approved.