What size nut is this?

[Kelpie]

I need to source a replacement for a nut. It looks very close to a 28mm standard plumbing part, but is a little smaller.
I'm guessing that it might be some sort of imperial size. Would 1" BSP sound right?
The diameter of the threads, inside the nut, is about 33mm.
Would post a photo if I wasn't a bit of a luddite...

 

[chewi]

I need to source a replacement for a nut. It looks very close to a 28mm standard plumbing part, but is a little smaller.
I'm guessing that it might be some sort of imperial size. Would 1" BSP sound right?
The diameter of the threads, inside the nut, is about 33mm.
Would post a photo if I wasn't a bit of a luddite...

I think you need to check your dimensions.
33mm dia is avery long way from 28mm and even further from 25.4 mm (inch)

 

[theoldsalt]

I need to source a replacement for a nut. It looks very close to a 28mm standard plumbing part, but is a little smaller.
I'm guessing that it might be some sort of imperial size. Would 1" BSP sound right?
The diameter of the threads, inside the nut, is about 33mm.
Would post a photo if I wasn't a bit of a luddite...

Possibly - see here http://www.tapshop.net/bsp_etc/

 

[superheat6k]

I think you need to check your dimensions.
33mm dia is avery long way from 28mm and even further from 25.4 mm (inch)

1 inch BSP refers to the internal diameter of the intended pipe the nut secures, so the OP is correct the ID and OD will be larger, but 1" BSP has a minor diameter of 30.3mm 33mm would be very sloppy.

So OP do you know the OD and preferably the pitch. To work this out count how many peaks occur is say 1/2" of thread and double it, or how many in say 10mm and divide it to get the pitch.

 

[Kelpie]

At the moment I only have access to the (cracked) nut, not the pipe itself.
I've tried screwing it onto a 28mm fitting and it will go a couple of turns, but clearly is not the right size/thread.

 

[PuffTheMagicDragon]

It sounds like a 1" BSP. This has 11TPI while a 7/8" BSP (your 28mm?) would have 14TPI. This would explain why the nut will only mate for two turns but will go no further.

 

[Lakesailor]

If it goes on a couple of turns it's the pitch that does not match.

(shit. Beaten to it

 

[Kelpie]

Hmm, counting threads is tricky. Doing it very roughly using a rubbish set of calipers, I get about 16tpi. If I'm measuring it right...

EDIT- using the same method, I get about 15tpi on my 28mm fitting.
The mystery nut is definately a finer pitch.

 

[Lakesailor]

I have a thread file for cleaning up the threads. Each of the 8 faces is marked with TPI. That makes matching up easier.

Try pressing some putty or similar into the threads in the nut and then measuring that.

 

[Kelpie]

Well, fortunately (?) the nut has actually split in two, so measuring the threads is easier than it would otherwise be. It was held together with tape which is how I was able to try it on a 28mm fitting and conclude that it wasn't a match.

 

[scottie]

Where is it used?

 

[Kelpie]

It's used to connect a tube housing a centreboard lift wire.

 

[Davegriff]

A good start would be to determine whether the nut is metric or imperial. If its original, it'll likely be the same as the rest of the boat, so age of boat or country of origin would be a clue.

 

[charles_reed]

Why not take the nut to a fixings company and ask them for an answer. We have a situation here of the short-sighted leading the blind and all will be guesswork.
If there are no fixing companies close-to-hand, you'll have to travel!!

 

[Kelpie]

It's an American designed, British built, boat from 1970. So would that point towards imperial?
I was just asking the question in the hope that there would only be a small number of possible answers, but it doesn't look that way....

 

[Lakesailor]

Why not take the nut to a fixings company and ask them for an answer. We have a situation here of the short-sighted leading the blind and all will be guesswork.
If there are no fixing companies close-to-hand, you'll have to travel!!

Apart from a decorating shop and a quarry I expect his options are limited.

 

[VicS]

It's an American designed, British built, boat from 1970. So would that point towards imperial?
I was just asking the question in the hope that there would only be a small number of possible answers, but it doesn't look that way....

If you measure the OD of the thread ( I take it 33mm is the core diameter/ ID of the nut) and the pitch in tpi or in mm it should be able to identify the thread from the tables available

Vernier, thread gauge and "Zeus" !