Abstract: A cluster of pins, serving to clean the surface of a workpiece, are slidably mounted in bores of a guide plate which is spring-urged against a metallic anvil, with formation of a clearance between the plate and the anvil in which the heads of the pins can move. The anvil is periodically struck by a ram which is freely reciprocable in a tool housing surrounding the anvil and the guide plate, the housing being provided with a pistol grip carrying a trigger that controls admission of compressed air to a chamber at the rear of the housing which is intermittently vented by the advancing ram to a space communicating with the atmosphere via channels in the anvil and perforations of the guide plate, thereby cooling the movable parts of the tool. The guide plate consists of a hard but light-weight resinous material, specifically polyamide 6.