A self-centring blocking device for wheels on turntables of tyre-changing machines

The device for blocking wheels on a turntable of tyre-changing machines comprises a hollow shaft (13) to a top of which is constrained a turntable (11) having a central opening in which a blocking pin (14) slides, which pin is provided with a truncoconical stopper (21) which engages superiorly with a central hole of the wheel rim (12). The pin is displaced and held in rim-blocking position by a pneumatic single-acting cylinder (22) and by means (28,29) for automatically constraining the pin to the cylinder. The blocking of the rim (12) is completed by a hinge mechanism for preventing rotation of the rim in relation to the table.