WR-04 is for Big Blue Water Filter Housing Spanner Wrench Compatible With Culligan / Ametek / US Filter / Plymouth / Kleen Plus / American Plumber / Bruner & Many Other Brands. WR-04 Big Blue 5 7/8″ Water Filter Housing Wrench. (Big Blue Filter Housings Use A 5 3/4″ Diameter “O”Ring) Ametek # 150296 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.