By inserting a protruding portion (8b), which is installed to a center position of a rear end surface (8x) of a fixed body (8), into a hole (4a), which is provided to a center position of an end surface (4x) on a side of a fixed body (8) of a fixed shaft (4) that is connected to a fixed body (3), the fixed bodies (3) and (8) and the fixed shaft (4) are connected. As a result, a sleeve (5) can be removed only by dismantling the fixed body (3).
