Description

The Harmsco 905 is the replacement cartridge retainer nut for the TF and TC series cartridge filters. It is listed for the TF50, TF75, TF100 and TF150, and for the 50TC, 75TC, 100TC and 150TC. It also appears as HRM905 in Harmsco parts listings.

What it does

The retainer nut clamps the cartridge down inside the housing. That clamping is what forces every gallon through the media rather than around the outside of it. When the nut cracks, strips or goes missing, the cartridge lifts under flow and the filter quietly bypasses, so the water stops clearing even though nothing appears to be broken.

Why it wears out

This is a part that gets handled at every service. It comes off for each cartridge clean and goes back on afterward, and repeated cycles of that eventually take the threads or split the body. Keeping a spare with your filter cartridges means a routine clean never turns into an unplanned trip for parts.