5/16" thread diameter, BSF (22 TPI measured with a thread
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
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
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.
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.
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.
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.
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.
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.
I haven't tried any of these small locals with bronze, as the original
fasteners are still fine after the 25 years
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.
For every complex problem, there is a solution which is simple, neat,
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.
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.
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.
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