A dripping single-lever tap is a worn cartridge, and the part is defined by its diameter and the shape of its base. 35 mm and 40 mm are the common ceramic disc sizes; the base and its locating pegs are what actually decide fit.
Why the cartridge is the tap’s real specification
It is the only moving part that wears, and it is what separates a tap you can keep from one you replace. A standard-diameter ceramic cartridge is stocked by everyone; a proprietary insert of an odd size is sold by one maker for as long as they choose to.
Taking the old one out
The lever comes off — usually a grub screw under a cap — then a retaining nut, then the cartridge lifts out. It goes back in one orientation only, and getting that wrong reverses hot and cold or blocks flow.
Buying the new one
Measure the old one across the ceramic body, and compare the base. Some makers publish a part number on the cartridge itself, which removes the guesswork entirely.
While it is apart
Look at the O-rings on the tap body. They are pennies, they harden, and they are the cause when a tap weeps around the spout rather than dripping from it.
Questions people actually ask
Is a dripping tap always the cartridge?
On a single lever, almost always. On a two-handle tap it is the valve head or its washer, which is a different and even cheaper part. A weep around the base of a swivelling spout is an O-ring rather than either.
Can I buy a universal cartridge?
Universal within a diameter and base pattern, yes — that is what most aftermarket cartridges are. Universal across every tap, no, and a listing that claims it is describing a size rather than a fit.
Last reviewed 5 September 2026