This is a replacement O Ring for the Shower Waste Dip Tube.

It inserts into a groove at the top of the Dip Tube which is just underneath the chrome cover.

It is essential for providing an air tight seal, 

which prevents foul air from entering the room from the drain system. 

This is an O ring type seal. Many waste fittings have a square profile seal instead of an O ring type seal. The two types of seal work in exactly the same way. This O ring should seal just as well as your old square one.

Listing is for the O'Rings Only and not the Shower Waste Drain Plug Itself!!!!!!