PURPOSE: To facilitate mounting and demounting of a shaft to and from the insertion hole of the grip in a grip-mounting method for a handle section, etc., of tooling, by closing the opening of the blind-hole like insertion hole of the grip by an end face of the mounting shaft, and supplying a compressed air into the insertion hole to enlarge the diameter of the insertion hole and mounting/demounting the mounting shaft.

CONSTITUTION: A large-diameter portion end is forced into an end opening of a shaft insertion hole 5 of a grip 2 to close the end opening. On the other hand, a normally closed type three-port valve 10 is mounted in a strap attachment hole 6 of the grip 2, and a compressed air is supplied into the shaft insertion hole 6 of the grip 2. As a result, the pressure in the insertion hole 5 closed by the large-diameter end of the shaft 1 rises, so that the inner diameter of the insertion hole 5 is enlarged. Accordingly, the shaft 1 can be easily mounted to or demounted from the grip 2. The three-port valve 10 is constructed such that a main body 11 thereof is provided, at one end of its outer periphery, with an insertion portion 25 being fitted into the strap attachment hole 6, the insertion portion 25 being provided, at, its fore end, with an out port 26 communicated with a screw insertion hole 7 formed in the bottom wall of the strap attachment hole 6.