American Standard Piston Assembly for Manual Toilet Flush Valve 1.28 GPF (Blister Pack 100) - AMS-M964905B-007

It is the internal piston that meters the flush on an American Standard manual (non-electronic) diaphragm-free flushometer. The piston is the wear part: when a valve starts running on, short-flushing, or won't shut off, this is the assembly you replace rather than swapping the whole flushometer. It ships as a blister pack of 100, which is a maintenance-stock quantity for a facility that standardizes on one valve, not a single-fixture repair kit.

This piston is built for 1.28 GPF manual toilet flush valves. The piston is what sets the volume the valve passes, so putting a 1.28 GPF piston into a valve you want running at 1.6 GPF changes the flush volume of that fixture. If the building is on 1.6 gallon water closets, order the piston that matches that rating instead.

No. It's a water closet part, rated 1.28 GPF for toilet flush valves. Urinal flushometers run at much lower volumes (0.125 to 1.0 GPF depending on the fixture), so the toilet piston will over-flush a urinal. Order the urinal-specific repair part for those valves.

Order American Standard M964905B-0071280A. The 1280 in the suffix is the flush rate, 1.28 GPF, which is the detail that separates it from the same piston built for other volumes. There is one configuration, supplied unfinished since it's an internal component with no exposed trim.

The M964905B-0071280A comes as a blister pack of 100. That quantity suits a hospital, school, stadium, or multi-family portfolio doing a standardized rebuild across a whole restroom group or holding shop stock for a valve type used building-wide. For a one-off repair on a single water closet, it's more part than the job needs.

If the valve body and the handle assembly are sound and the complaint is running-on, weak flush, or failure to close, the piston is the part that has worn and a piston swap restores the valve at a fraction of the labor of pulling and re-piping a flushometer. Replace the whole valve when the body is damaged, the supply connection is compromised, or you're changing the flush volume the fixture is rated for. For fleets, keeping this piston on the shelf in a 100 pack is what lets a maintenance tech close the ticket the same day.