To make it possible to prevent a protrusion such as burr or the like left on an inner peripheral surface of a cylindrical part from biting into an outer peripheral surface of a shaft part and to prevent the shaft part from being hardly pulled out of a cylindrical part.

There are provided a pair of cylindrical parts 10, 20 having screw holes 12, 22 into which two opposing shafts 101, 102 are inserted, respectively and penetrating in a direction orthogonal to axial directions AX of the shafts 101, 102; a connection part 30 for connecting the cylindrical parts 10, 20 to each other; and set screws 40, 50 that can be threadably connected to the screw holes 12, 22 and having their extremity ends capable of being abutted against outer peripheral surfaces 101a, 102a of the shaft parts 101, 102. Inner peripheral surfaces 10b, 20b of the cylindrical parts 10, 20 are provided with recesses 13, 23 spacing apart the screw holes 12, 22 from the outer peripheral surfaces 101a, 102a of the shaft parts 101, 102.