Looking for some nuts, bronze ones.

5/16" thread diameter, BSF (22 TPI measured with a thread gauge).
These are for the stern gland on the prop shaft of my little sailing boat. We don't like to use dis-similar metals under the waterline due to the possibility of galvanic corrosion.
I managed to make one of these nuts round due to over tight- ening with a wrong size spanner, had to take it off with a nut splitter.
Any suggestions where I may find nuts matching the above description? I've spent quite a while Googling and all the hits I've come up with are either 5/16" nuts in mild or stainless steel, or brass (sometimes bronze) nuts in the wrong size.
Regarding the dis-similar metals, and me making one round, I was under the impression that bronze (silicon-bronze) was quite hard, I would have thought that to be this soft they were brass. Any thoughts on this?
All suggestions gratefully received. Oh, once I've got replacement nuts I shall find a spanner that's a very good fit and save it for this purpose. I don't want to go through this trouble again.
Justin.
--
Justin C, by the sea.

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On Tue, 23 Apr 2013 15:21:22 +0100, Justin C wrote:

Some cars used to use brass nuts to hold the exhaust downpipe to the manifold - maybe there's an avenue for you to try ?
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I can confirm that those brass nuts were soft and easily rounded :-( (I can't comment on bronze ones.)
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When I was building our boat 25 years ago, I bought a lot of the bronze screws and nuts and bolts from the Clerkenwell Screw Co in Clerkenwell Rd in London. It was quite a long walk from there to Euston Station and they were quite heavy! The man there was Canadian and really helpful. When I last asked them about something 2 or 3 years ago, they didn't seem as good and didn't understand what I wanted, but they might be worth a try.
I think bronze comes in many varieties, but I'm no expert. Brass beneath the waterline would last no time at all.
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Bill

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On 23/04/2013 16:03, Bill wrote: ...

Unless it is Admiralty brass or naval brass, which have tin added to stop de-zincification.
Colin Bignell
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On 23/04/13 16:03, Bill wrote:

He retired long ago (10+ years?) and the business was sold to some Indian gentlemen.

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... who doesn't appear to have a web-presence - at least, not one that is easily found.
Thanks anyway.
Justin.
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On 23/04/13 15:21, Justin C wrote:

http://www.allfix.co.uk/Products/Full-Nut-Brass-Imperial/NUFL1SCB031

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Thank you, TNP. I did find that site early in my search but I understood they only sold in quantities of 1,000. I've looked again and realise I was mistaken. I shall order while I investigate having some machined in bronze for me.
Justin.
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You need aluminium bronze
google "aluminium bronze nut" and it brings up a couple of UK based suppliers.
Alternatively head over to news:uk.rec.models.engineering and someone might have some on the shelf and be able to make you a couple for a few beer tokens.
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On Tue, 23 Apr 2013 16:31:12 +0100, The Other Mike
some *hex bar* on the shelf
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I thought it was silicon bronze... but, after some Googling, I believe it's either.

That's not a bad idea. I've found an engineering firm that will do it, but I don't yet know price or minimum quantity. I doubt it can be cheap. It may be cheapest to try the brass first and keep a close eye on them.
Thank you for the suggestion.
Justin.
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I repeat that if it is at all likely to come into contact with sea water, do not use brass except on a very temporary basis. It crumbles into powdery copper. Silicon bronze is the material. Stainless steel might be OK with regular checks.
Our local small engineering shop made my 316 stainless steel prop shafts and I was very happy with the price. I have called in very occasionally since then and they have made small things for me for remarkably low prices or in one case "not worth the paperwork" free.
I get stainless steel from local non-ferrous scrapyards, and know a different local metal bashing firm who are excellent and cheap for the bending and welding.
Small engineering places are hard to find, but well worth supporting. There are also big firms with reception areas and lady receptionists. Avoid them.
I haven't tried any of these small locals with bronze, as the original fasteners are still fine after the 25 years
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On 23/04/2013 15:21, Justin C wrote:

I was under the impression that a lot of boat stuff was made out of 316 stainless these days. I wonder what the studs are made from. You have to be a bit careful with stainless nuts and bolts because they can seize up owing to galling. On the other hand, well finished ones with suitable clearances can work well. (Sometimes they are plated). When you say under water, are these only accessible from outside, or are they in the bilges and therefore wet some of the time. There are thread lubricants which work quite well on stainless and these might survive in the bilges although they are more likely to get washed away on the outside.
I think the suggestion elsewhere to try on the model engineers group is a good one.
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Most stuff is, unless it's submerged. I found some nice crevice corrosion the year before last, that's what eats stainless.

I believe it's bronze. There are major problems with metal below water, galvanic corrosion. Bronze being a 'more noble metal' lasts longest, and it helps to have sacrificial anodes (zinc in seawater, can't remember what they use in fresh water).

I see that I may have been unclear on this point. The whole fitting (stern gland) is below the water, half of it is inside the boat and half outside. I believe it's all bronze outside and mostly bronze inside, with the possibility of these nuts being brass. The stern gland is what keeps the water out of the boat at the point where the propeller shaft exits the hull. These nuts should very rarely be submerged (very, very rarely).
I'm completely lacking in understanding of the galvanic corr- ossion. I've tried to get my head round it but it seems to be a subject that the experts don't all agree on. So, should I use brass or not? I don't know, but if they fail after a while I'll know, and I can easily keep an eye on them, so unless I can actually get bronze I shall be using brass.
Thank you for the reply.
Justin.
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On 23/04/2013 18:41, Justin C wrote: ...

The problem with brass in seawater is not galvanic corrosion, but that the zinc leaches out of the metal, leaving a porous, weak matrix of copper behind. If the nuts will normally be dry, that may not be much of a problem, but keep an eye out for them starting to look reddish. There are brasses that have tin added to reduce the risk of zinc loss, so, if you can get naval brass, that will be better than plain brass, while, as others have said, aluminium bronze will be best of all.
Colin Bignell
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[snip]
Thanks to all who responded. I'm going to go with brass and just keep an eye on them. I've had a good Google for bronze and I can't find anything UK without having something made. I will enquire, and if they're cheap enough I'll order some, but for less than a fiver I can have something that should do, enough to get me afloat at least.
Justin.
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Justin C wrote ...

http://www.jcooke.co.uk/page2516/standard-nuts.aspx
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On Tuesday, April 23, 2013 7:11:55 PM UTC+1, Justin C wrote:

Is there some reason why you can't use a tap to make your nuts?
NT
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I don't have the tools, nor the raw material. Nor do I have a workshop where I could do such a thing. It's a skill I'd love to be able to develop.
Justin.
--
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