Leaking sink trap - which washer?

[Old UKPF 121121]

I have a dripping sink trap which it seems needs a replacement washer. Sink trap kits I've found contain the right type of washer - a flat O-ring, but the sizes tend to be 32mm or 40mm. The 32mm are a bit small and the 40mm way too big. Any idea what I should be looking for?

 

[Deleted member 120897]

Trap Inlet Washer 38mm - https://www.toolstation.com/trap-inlet-washer/p90882. You mention flat o-ring, is it a specific type of trap?

 

[Old UKPF 121121]

Trap Inlet Washer 38mm - https://www.toolstation.com/trap-inlet-washer/p90882. You mention flat o-ring, is it a specific type of trap?

Not sure, I took out the current washer and described it as best I could - the type you linked to looks to be the right kind of thing, though possibly a little large if 38 mm is the internal diameter, although I guess I could order a bunch of these in varying sizes to see if I can get lucky and find one that fits.

 

[Old UKPF 121121]

Trap Inlet Washer 38mm - https://www.toolstation.com/trap-inlet-washer/p90882. You mention flat o-ring, is it a specific type of trap?

Using my own crude measurements I think I need one of approx 34mm (or thereabouts). Not having much luck finding one online so far - it seems an odd size

 

[cjg]

just go to local plumber merchants there will hve spares.

 

[Deleted member 120897]

Using my own crude measurements I think I need one of approx 34mm (or thereabouts). Not having much luck finding one online so far - it seems an odd size

Sounds like a basin one then, as opposed to kitchen sink.