Abstract: A tire air valve (core) mounting and dismounting tool 20 includes a tool head portion 21, a shank portion 22 and a grip portion 23. The tool head portion 21 has a slot 32 for seizing and holding a valve core head portion 16, an axial bore 33 for accepting a valve core shaft portion 14 and its enlarged end 14a. The tool head portion 21 also has annular groove 34 formed along a cylindrical peripheral surface thereof. Balls 36 are retained in second bores 35 which are open to the annular groove 34 and also communicate with the axial bore 33 through openings 37 of a reduced diameter to allow the balls 36 to partially protrude into the axial bore 33. A coil spring 38 is anchored and fastened in the annular groove 34 to act to normally bias the ball 36 radially inwards and leave the balls 36 protruding into the axial bore 33.