Monument Universal Radiator & Valve Key the ends are tapered and therefore self restricting.The three profiles make the tool universal, catering for 3/8 in and 10 mm square section radiator vent plugs and bleed screws. Bayonet or internal lug type radiator valves allowing for variations in size, shape and position. 12 mm to 14 mm internal hexagon valves tapered allowing for variations in size.