We have been asked this question several times, and it can be extremely confusing. There are 3 different versions of the Mansfield model 160. The most common version is the standard 160 with a tower style flush valve in the center that has a red seal at the bottom side of it, and uses the Mansfield 40 trip lever. One of the other versions of the model 160 is the 173. This model would use a 2 inch blue rubber flapper, and the Mansfield 31 trip lever instead of the tower, and the 40 trip lever. The last version of this toilet would be a model 3173. The 3173 also uses a blue rubber flapper, and the 31 trip lever, but unlike the 173 this version would use a 3 inch flapper. All three of the versions we have talked about are interchangeable. If you have the 211-1112 tower style flush valve in the tank, and would like to change to the flapper style flush valve you would need to purchase the 173, or 3173 complete rebuild kit. The reason you would have to replace all of the components inside of the tank is due to the lever, and flush valve. If you only replace the flush valve the trip lever will either hold the flapper up consistently, or if you are using the tower style flush valve it will hold the valve on an angle, and allow it to leak.