It is mostly using Undersink Water Purifier, Undersink UV Water Purifier, RO Water Purifier and other series of Water Filter. WR-03 Water Filter Housing Spanner Wrench Compatible With Culligan / Ametek / US Filter / Plymouth / Kleen Plus / American Plumber / Bruner & Many Other Brands. SW-2 Standard Size Water Filter Housing Wrench. Fits 4 3/4″ Standard Size Filter Housings. (Standard Size Housings Use a 4″ Diameter “O”Ring) Ametek # 150295 – Only for use in loosening filter housings, never to tighten. Overtightening 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.