Ideal, if you're 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 valve / ball-cock supplied with many Armitage and Ideal Standard toilet cisterns.
Univalve diaphragm - suits the newer twist cap style of inlet valve / ball-cock supplied with many Armitage and Ideal Standard toilet cisterns.
May have white or red plastic centre nipple (apparently this is a colour coding system used in the factory to identify different batches).
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.