Damage Free Restoration The removal of the NOX sensor usually causes damage to the threads as a normal tap is too long, and it might be placed at an angle that provides the new sensor with an incorrect mounting position within the exhaust. The damage can also be caused by the high variation in temperature and carbonization. The WELZH tap allows for damage free restoration of the NOX sensor hole thread, with the alignment guides ensuring it is at the correct angle. Extra Short Can be used with a socket or ratchet for hard to reach areas. Time and Money Saver No need for a new exhaust system. Universal For diesel particulate filter, any exhaust sensors, and those in a catalytic convertor.