To provide a solid and stable assembly by preventing a play in relative rotation operation between an outer cylindrical body and an inner cylindrical body to ensure proper rotation resistance feeling and preventing assembly deterio ration of a mounting cylinder assembled on the upper end of the outer cylindri cal body.

An elastic ring 15, in which a slide-contact projecting part 18 in pressure-contact with an outer peripheral face of an inner cylindrical body 10 is provided on the inner peripheral face of the upper part thereof is assembled on an outer cylindrical body 2 in a state, in which a lower part thereof is nipped and held by a screw cylinder 3 and an outer mounting cylinder 5 from the inside and the outside to prevent the elastic deformation due to the action of pressing force of a mounting cylinder 8 on the elastic ring 15, to eliminate a play due to the elastic force of the elastic ring 15, and to prevent the elastic deformation for assembly from affecting on an action part of the elastic ring 15, thereby obtaining proper elastic action of the elastic ring 15.