For all permanent mount RV toilets; fits standard 3" opening. Compresses to form a watertight seal between the toilet and the floor flange. Any time you install or reinstall a toilet, this seal should be replaced.  New toilets come with a seal so you need to buy this only if you are keeping your old toilet but removing and reinstalling.

4-7/8" Outside Diameter
3-1/4" Inside Diameter