American Standard Cadet3 3IN Toilet Flapper Assembly - AMS-738920

That's exactly what the 738920 is built for. It's the 3 inch flapper assembly for American Standard Cadet 3 tanks, ordered as part number 738920-0070A. If the flapper you pulled out is the smaller 2 inch style, this one won't seal against your valve seat, and measuring the seat opening on the tank bottom is the quickest way to tell the two apart before you order.

Only for the 3 inch Cadet 3 models. The 738920 flapper is specific to that valve size and to 1.6 gpf tanks, so it standardizes across Cadet 3 openings but won't cover American Standard toilets built around a 2 inch flush valve. For a mixed fleet, sort the units by flush valve diameter first, then stock this one against the 3 inch group.

The Cadet 3 flapper assembly is a 1.6 gpf part. If your tank is a 1.6 gallon per flush Cadet 3, this is the matching flapper and it will hold the factory flush volume. Swapping in a flapper meant for a different volume is how a tank starts running long or short on each flush, so match the rating rather than just the diameter.

No additional parts come into it. The 738920 is a drop in replacement assembly for the Cadet 3 flush valve: shut the supply, flush the tank down, unhook the old flapper and chain from the valve ears and the flush lever, and hang this one in its place. At 0.22 pounds it is a hand tool free swap in most cases. The chain length is what you set at the end, and it's the one adjustment that decides whether the tank seals or keeps trickling.

It ships as an assembly, not a bare seal disc, and it's catalogued by American Standard as a repair part under the 738920 number. The piece measures 5.3 by 4.1 by 2.6 inches and weighs 0.22 pounds, which is the whole flapper unit including its frame, not a trim ring.

There's one version only, no finish choice to make. The flapper is a functional tank part that sits below the water line, so it ships as a single configuration under 738920-0070A with nothing to specify on the order beyond quantity.