The Mansfield 160 tank comes with a few different types of flush valves. The most popular being a 211-1112 flush valve. This flush valve is the tower style flush valve with the red seal instead of a flapper. If you have the tower valve it uses the model 160 toilet parts. There are two other versions of the 160, one being a 2 inch flapper which is model number 173. The 2 inch flapper will measure 3 inches across the top, however if you measure the hole the flapper covers, it will be 2 inches. The other option that could be in your 160 tank is a 3 inch flapper. This would be model 3173. The 3 inch flapper will measure closer to 4 inches across the top, however measuring the hole that the flapper covers, would measure three inches. See below for a link to each depending on the flush valve you have.
