A coupling pin for fastening together multiple sections, said pin comprising: a carriage member; and a riding member, said carriage member and said riding member having respective planar inner surfaces (64, 66) mutually inclined longitudinally, said carriage member and said riding member together complementing each other to form a uniform pin, wherein said pin is configured to be inserted into aligned apertures formed through said sections, characterized in that said pin is configured to be displaced into a load-bearing position by an external axial force applied at one end of said riding member, whereby said carriage member substantially overlaps said riding member, and said pin is configured to be displaced into an insertion/retraction position by an opposite external axial force applied at the other end of said riding member, whereby said carriage member is axially shifted with respect to said riding member such as to form at least a rear protrusion of said riding member in said insertion/retraction position, wherein at least one of said carriage member and said riding member comprises: (i) a rear support ring, adapted for positioning and securing said riding member to said carriage member; and (ii) a front support ring, adapted for positioning and securing said riding member to said carriage member, and wherein said riding member is restricted in axial and rotational motion by at least one of: said rear support ring; and said front support ring, while in said load-bearing position. a carriage member; and a riding member, said carriage member and said riding member having respective planar inner surfaces (64, 66) mutually inclined longitudinally, said carriage member and said riding member together complementing each other to form a uniform pin, wherein said pin is configured to be inserted into aligned apertures formed through said sections, characterized in that said pin is configured to be displaced into a load-bearing position by an external axial force applied at one end of said riding member, whereby said carriage member substantially overlaps said riding member, and said pin is configured to be displaced into an insertion/retraction position by an opposite external axial force applied at the other end of said riding member, whereby said carriage member is axially shifted with respect to said riding member such as to form at least a rear protrusion of said riding member in said insertion/retraction position, wherein at least one of said carriage member and said riding member comprises: (i) a rear support ring, adapted for positioning and securing said riding member to said carriage member; and (ii) a front support ring, adapted for positioning and securing said riding member to said carriage member, and wherein said riding member is restricted in axial and rotational motion by at least one of: said rear support ring; and said front support ring, while in said load-bearing position. (i) a rear support ring, adapted for positioning and securing said riding member to said carriage member; and (ii) a front support ring, adapted for positioning and securing said riding member to said carriage member, and wherein said riding member is restricted in axial and rotational motion by at least one of: said rear support ring; and said front support ring, while in said load-bearing position.