Replacement piston assembly for WaterSoft Isobar 1 filters manufactured prior to 2010 (blue valve body).  If your filter has an orange cap like this one, then you need to use this piston.

If your piston has a White Cap, you need the 20561X254

If your piston has a Black Cap, you need the 20562X254

 Note: We recommend installing a new seal & spacer kit anytime a piston is being replaced.