To provide a fastener for mounting a rack member, article suspending pipe, etc., in a strut very easily and firmly without necessity for a machine screw, bolt, screw spike, etc.

This fastener comprises a strut 1 provided with a hole, outer ring 5 fitted to the outside of this strut and a lock receiving member 3 inserted between these outer ring 5 and strut 1 to lock receive the outer ring 5, the outer ring 5 is formed with a protruded part in the inside, the lock receiving member 3 is formed with a protruded part inserted to the hole of the strut 1, also a protruded part for lock receiving the protruded part in the inside of the outer ring 5 is formed. The protruded part of the lock receiving member 3 is inserted to the hole of the strut 1, the lock receiving member 3 is left as mounted, by only fitting the outer ring 5 from upward of the strut 1, the outer ring 5 and the strut 1 can firmly be fixed by the protruded part in the outer ring 5 and the lock receiving member 3.