Abstract: A method of assembling a lower receiver and an upper receiver of a firearm is disclosed. The method comprising steps of providing a threaded fastener; inserting the threaded fastener into a ratchet handle; mounting a ratchet gear into the ratchet handle, wherein the threaded fastener passes through an aperture of the ratchet handle and threads into the ratchet gear; positioning a locking plate at the lower receiver, wherein the locking plate is fixed to the ratchet handle by turning and tightening the ratchet handle with the engaged ratchet gear for locking to the locking plate in a locked position; and on the opposite side of the lower receiver, inserting a threaded pivot pin into an aperture of the locking plate from the opposite side of the lower receiver, wherein a threaded rod of the ratchet gear is threaded into a threading cavity of the pivot pin.