Armitage Shanks / Ideal Standard Univalve quiet WC toilet cistern inlet / fill / ballcock / float valve diaphragm washer.
Suits the newer Univalve twist cap style of inlet valve / ballcock supplied with many Armitage Shanks and Ideal Standard toilet cisterns. It will not fit the older Hushflow screw top valve.
May have white or red plastic centre piece (this is a colour coding system used in the factory to identify different batches). Currently they are supplied with a white insert.
Please study all picture(s) very carefully to make sure you are buying the correct washer.
When these washers are new they have a smooth surface. After they have been used for a while they develop 18 little ridges pressed into the rubber.