HWR-20 Full Circle Wrench for Water Filter Replacement of Standard Size Housings Designed to fit perfectly to 10-inch or 20-inch long standard size housings to replace 2.5-inch dia filter cartridges, compatible with most of the standard size water filter housings, made with durable, strong plastic material in full circle shape, the inner diameter of the wrench is 3-3/4 inch between shortest points.