To provide a joint whose strength is enhanced so as to prevent a hook from becoming dislodged from a dovetail-grooved frame by allowing it to be bent in the inward direction in which a pair of supporting pieces approach each other at the time of driving a wedge, and capable of securely fastening even an ovally-shaped part of a pipe without loosening.

Non-slip pieces 24, 24a, 24b and 24c cut-and-raised and bent toward the downside are provided in between coupling pieces 9 and 10 for coupling a pair of supporting pieces 7 and 8.