Culligan SW-1 Housing Wrench 3/8", Undersink Water Filter Housing Wrench. 3/8 inches Undersink Water Filter Housing Wrench Housing Wrench 3/8" Wrench Use the SW-1 wrench to loosen bottom of housing during cartridge replacement. Slide circular end over housing until a snug fit and unscrew. Do not use the SW-1 wrench to tighten the bottom of the housing. Only hand-tighten the bottom of the housing onto the cap to prevent cracking. The SW-1 makes changing water filters easy.SW-1 and SW-1A assure you that the product is the same, and the listing is correct, as the product is a direct comparable to the Pentek-SW-1 The SW-1 spanner wrench can be used with Slim Line and 3G housings. The SW-1 wrench is approximately 4.25-Inch Wide. (Note: Width is slightly less at the notches.)