Tap washer diameter

[Mungo Henning]

Okay, what gives: someone educate me please? My kitchen taps started to drip recently, so I turned the water off and unscrewed the tap. The washer was 16mm in diameter. I didn't have any spares in the spares box hence I did the usual trick of reversing the washer as a temporary fix.

So I then toddled to B&Q and eventually bought a cheapo pack of six washers (three pairs of washers of each diameter). Once back home, the washer labelled "three eighths" was the one that matched. Since an inch is

25.4 mm, one eighth ought to be a smidge over 3mm hence three of these works out at 9mm. Nowhere near the 16mm necessary.

So how have I muddled the sizes - anyone know?

Mungo (hoping that I haven't goofed too badly on this post)

[Roger]

The message from "Mungo Henning" contains these words:

I think it is probable that the 3/8" is the pipe size but I am not certain of that. Seems reasonable to me though. You would need 5/8"+ to cover a seat with a bore of 3/8".

[newshound]

In the good old days, one size washer fitted all sink taps and another all bath taps. This no longer seems to be the case. Check out the BES washer kit.

[Owain]

And we had sink plugs and bath plugs.

Owain

[nightjar]

A 3/8" washer fits a 3/8" tap. Tap sizes are based upon the bore of the feed pipe. That will also be the size of the hole the water enters the tap body through. The washer needs to seat onto a rim around that hole, so it has to be larger

Colin Bignell

[Mike Clarke]

And it's well nigh impossible to find anywhere that sells replacement O-rings to fit the metal plugs.

[Mungo]

Hi Colin, Ta for the reply (but)...

Err... in these days of metric, the above (IMHO) is not that useful.

I've got 15mm pipes feeding the taps, but they narrow down for the monobloc tap thinggy.

Again (and also for the other kind repliers): what gives? How come the caliper gauge measures the old washer as 16mm diameter yet I have to go and buy a three-eighths washer?

Mungo

(politely: please no more advice on where to buy a suitable replacement washer. As my original post said, the job is done, but I want to know *why* I need to buy a three-eighths washer for a 16mm diameter job?)

[nightjar]

Steel and plastic pipes are still identified by the bore in inches, although the standards now give their dimensions in mm, as are many fittings. Only copper is properly identified by the OD in mm.

The tap size is based upon the assumption that it has a British Standard Pipe threaded connector, whether it actually has or not. That thread would match the size of thread that could be cut on the oustide of a steel feed pipe of the relevant size, in this case a 3/8" bore pipe. BSP is a metric standard thread, even though it refers to inch sizes.

Measure the hole in the middle of the seat that the washer fits to. That should be 3/8". You will find the same applies to 1/2" and 3/4" washers - they are larger in diameter than the tap size marked on them.

Colin Bignell