The closet flange is the plumbing fitting with the very noble and unpleasant task of connecting a toilet to a drain pipe. The name comes from the oval headed closet bolts that lock into the closet flange and hold the toilet in place. Boeing 747 toilet A toilet is a plumbing fixture and a disposal system primarily intended for the disposal of the bodily wastes urine, feces, vomit and menses as well as most of this article. ...

The closet flange is a flat disc attached to the floor, under the wax ring. For proper seal with the toilet, it must rise 1/2 inch above the finished height of the floor - if you're installing tiles, be careful you don't end up with a recessed flange. If the finished height doesn't leave the flange 1/2 inch above the floor, you will end up with a recessed flange and eventual leak. Go to Home Depot, Lowes, Ace, whatever and get a closet flange extension, which is bolted on top of the existing flange to achieve a good seal.

Flanges are typically supplied with 3 inch or 4 inch fittings, available to connect to a wide variety of pipe types: plastic (check the markings on the pipe to see if it's PVC or ABS!), copper/brass (usually in commercial buildings because it's non-combustible and will contain a fire), iron, or finally clay. Iron and clay are generally found in older buildings.

Note, of course, that almost all plumbing pipes are sized by the INSIDE dimension.

The flange itself is a flat disc with a hub fitting. (A hub fitting is the same size as a pipe of the same size and can therefore be connected directly to plumbing elbows, couplers, etc. of the same pipe size.) Another option is an "inside flange". An inside flange is a flange with a smaller discharge fitting, which can be used to retrofit a new flange onto older pipes. Oatey (a major plumbing supplier) makes models which are specifically designed to be inserted into existing pipes. They work well, though because the nozzle is inherently smaller (given pipe diameter less wall thickness), all inside flanges should be viewed as a last resort because of potential clogging issues (especially with ineffective 6L "water efficient" toilets which require 4 flushes).