For connecting trusses. There is one circular hole in one end of the pin. Insert the safety detent while installing so as to preventing the pin form dropping. There is a socket in the pin top, with the direction in conformity with that of small circular aperture. While installing, make the socket parallel the upper & lower chord member, so that the safety detent may be inserted into the pin smoothly. While erecting triple-row bridge, for the convenience of assembly & removal,