Washers for most taps above come in standard sizes. However, some modern taps do without washers altogether or may have different seals.

Do modern taps have washers?

Nowadays, the vast majority of modern bathroom taps use ceramic disc cartridges instead of rubber washers. In simple terms, this means no (or at least far fewer) leaks, and only a 90-degree rotation to turn the tap on or off. Back in days of old, taps and shower fittings always used rubber washers to prevent dripping.

Do all taps have a washer?

It will all depend on the type of tap you have installed. A traditional tap will use a tap washer. Whereas, something like a Monobloc tap (a type of mixer tap,) will use a ceramic disc, housed in a cartridge. These parts are likely to need replacing to stop a dripping tap.