If you are not sure which washer to buy, this pack includes both old and new types of washer :
Hushflow diaphragm suits the older screw cap (quiet) style of inlet / fill / ballcock / float valve supplied with many Armitage Shanks and Ideal Standard WC toilet cisterns.
Univalve diaphragm suits the newer twist cap style of inlet valve / ballcock supplied with many Armitage and Ideal Standard toilet cisterns.
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.
When the Univalve washers are new they have a smooth surface. After they've been used for a while they develop 18 little ridges pressed into the rubber.