Abstract: A pneumatic screwdriver incorporates a torque limiter for cutting off the supply of compressed air when the torque reaches a particular threshold. The invention includes a first positive clutch connected to a drive shaft and a second positive clutch connected to the tool. These components have three teeth offset by 120.degree. facing each other with a groove in the teeth in which there is a boss. Balls are inserted between the positive clutches in order to separate them when the torque is reached to shut off the admission of compressed air and then escape from the bosses so that the teeth rub on each other to brake the drive shaft.