preassembled self - locking guide and pivot pin cartridge assemblies are installed on the job site in folding doors rather than on the factory assembly line . considerable labor is saved in manufacturing and a better installation is achieved . both the guide and pivot pin assemblies feature molded nylon housings which conveniently snap into place on the folding door brace structure . top and bottom guide pin assemblies are identical and interchangeable . a lower adjustable pivot pin assembly possesses more than one and one - half inch of full threads on the molded nylon housing and includes a hardened steel lock clip having snap on engagement with the housing and threaded engagement with the adjustable screw - threaded pivot pin . a cooperating lock nut is provided to secure the assembly after proper adjustment . both of the guide and pivot pin cartridge assemblies are insertable as units on the doors and can be removed if necessary .