Abstract: A joining structure for coupling and pipes in frames used in bicycles and similar vehicles including engaging projections formed on either connecting projections of the coupling or the pipe ends, and insertion cut-outs formed in the mating connecting extensions or pipe ends. After insertion, the mated parts are rotated until they are machanically locked in place by locking slots. Bonding agents may be used to increase the strength of the joints and/or intermediate parts can be used to securely join the connecting extensions and pipes by the use of locking slots and the application of bonding agents. The design provides overlapping in the joints between the intermediate parts and the pipes to increase the bonding surface area and thus the mechanical strength.