6" in diameter. Fits #20 big blue whole house water housings with 6 ridges. Replaces the plastic SW-4 wrench Fits the following housing : American plumber W2010-PR / 152015/ W2015-PR / 152017 / 152022 / 144368, Pentek 150237 / 150239 /150469, Pentek BBFS-22, Pentek 144368, Ametek Kleen-Plus 144368, ...