Abstract: A device for coupling a pair of square bars made of metal or some other material and arranged squarely in abutment relative to each other at a squarely abutting corner of the bars can remarkably reduce the time and effort required for the coupling operation and improve the coupling strength with which the square bars are coupled to each other and also the appearance of the coupled area. When coupling a pair of square bars, the first and second square bars provided respectively with first and second anti-release grooves are arranged to abut each other rectangularly and the first and second engagement sections of the inner joint are loosely put into the first and second anti-release grooves respectively.

Abstract: A device for coupling/fastening a pair of square bars made of metal or some other material and arranged squarely in abutment relative to each other at a squarely abutting corner of the bars can remarkably reduce the time and effort required for the coupling operation and improve the coupling strength with which the square bars are coupled to each other and also the appearance of the coupled area. Such a device can find a variety of applications. When coupling a pair of square bars, the first and second square bars 1, 2 provided respectively with first and second engagement/anti-release grooves 1b, 2b are arranged to abut each other rectangularly and the first and second engagement sections 3a, 3b of the inner joint 3 are loosely put into the first and second engagement/anti-release grooves 1b, 2b respectively.