PURPOSE: To prevent looseness from occurring even after repetitive use and to facilitate its assembly for improvement in working ability by machining a screw thread having a shape enlarged in volume on a rubber so as to frictionally come into contact with a mating screw.

CONSTITUTION: A metallic nut 6 is fixed to a casing 7, and a rubber member having a machined internal thread 5 into which a piercing external thread 4 bites is provided on the surface of the internal thread part of a nut 6. Thus looseness does not occur between the internal and external threads after its repetitive use, work can be simply inexpensively executed.