C Shaped Open End Filter Wrench – Universal “C” style wrench for all standard size and Slim line water filter housings. 3 5/8″ opening. Only for use in loosening filter housings, never to tighten. Over tightening may cause damage to the O-rings and make re-opening VERY difficult. Hand tighten only. For really stubborn filter housings our technicians will use two wrenches together for maximum power where one wrench might break or not do the job. Our techs know the tricks.