It is Slim Line Water Filter Housing Spanner Wrench Compatible With Culligan / Ametek / US Filter / Plymouth / Kleen Plus / American Plumber / Bruner & Many Other Brands. WR-01 Water Filter Housing Wrench. Fits 4″ Slim Line Housings. (Slim Line Housings Have A 3 1/2″ diameter “O” Ring) Ametek # 150294 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. Fits most standard style RO systems. Replaces 150294. 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.