Abstract: An improved pin assembly for forming at least one pin joint in an object. The pin assembly may be readily inserted into and removed from more than one object when forming a pin joint, without the need for any special tools or equipment. The pin assembly comprises an unthreaded, self-locking pin comprising a first end and a second end; an elongated shaft; a hole intersecting the shaft; and a fin slidably disposed in the hole. The self-locking pin is configured to be readily inserted into and readily removed from an object, wherein the object comprises at least one first aperture on at least one first space frame member and at least on second aperture on at least one second space frame member. The fin is in its extended position after the self-locking pin is inserted through both the first space frame member and the second space frame member.