Thread sizes

Alec_t · 15 Oct 2025

Is the thread size of nuts on 15mm compression fittings (specifically isolation valves) in the UK standardised, or does it vary with manufacturer?

terryplumb · 15 Oct 2025

Virtually all are 1/2 inch BSP thread. Prestex fittings historically used a different thread ,not sure about now.

cross thread · 15 Oct 2025

Nearly all 1/2 inch BSP

Exedon · 16 Oct 2025

terryplumb said:
Virtually all are 1/2 inch BSP thread. Prestex fittings historically used a different thread ,not sure about now.

Prestex went over to 1/2 in BSP must be 30 or more years ago.
Still find the odd fine threaded one on old pedlar Belmont & terrier rad valves.

Alec_t · 16 Oct 2025

Thanks guys. I was hoping to do a quick swap of an isolation valve, re-using the old valve's nuts and olives. I'm guessing the old (weeping) valve dates back 10 years or so. Doesn't look like a Prestex one.

Leftum · 17 Oct 2025

Alec_t said:
Thanks guys. I was hoping to do a quick swap of an isolation valve, re-using the old valve's nuts and olives. I'm guessing the old (weeping) valve dates back 10 years or so. Doesn't look like a Prestex one.

You’d be unlucky if it’s not 1/2 inch. Use a bit of thread paste on the old olive if you don’t change it.

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Thread sizes

Alec_t

terryplumb

cross thread

Exedon

Alec_t

Leftum

DIYnot Local

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