do I need a Whitworth, BSF or UNC nut?

Burnham Bob

Burnham Bob

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My gooseneck is held on by a threaded metal piece that includes the rams horns and a captive shackle for the sail foot.

After removing the boom for a repair last season, I replaced it and tightened up the nut, and through the hole in the nut and threaded post stuck a split pin (the previous arrangement) to stop the nut working loose.

Wasn't quite tight enough - the shackle and rams horns revolved a bit under pressure. So this season I thought I'd use a nyloc nut and tighten up hard without bothering where the hole was.

Trouble is when I went to get a nyloc nut the thread isn't a normal thread available these days. So, its a Kemp mast and boom on a 1978 boat - what thread do forumites think it might be? It's a 3.8ths something or other....... individual imperial nyloc nuts are pennies on ebay so I don't mind ordering a few.
 
Best way is to borrow a Vernier and a thread gauge and measure.
Alternatively get a plain nut of each type and see which fits.
Nonetheless, having said that I would venture to say that a 1978 nut on a Kemp spar would most probably be BSW.
 
Be wary - many BSW and UNC threads appear to be of similar diameter and pitch; the nuts seem to be interchangeable, but the profile of BSW and UNC threads are markedly different and using one the other will result in a loss of strength.

I go with PMD on tis one, on a Kemp mast of that age, almost certainly BSW.
 
I have redrawn a simple table which I have used for many years, ere (hope it works fingers crossed):

View attachment Thread pitch table.doc

One old motorbike will often have this range of screw forms plus some that have yet to be classified by humanity.
You only need to look at the first 4. BSW and UNF can be mixed as pointed out by Minchsailor, this should be no problem in your application.

You can get thread gauges, to measure the things, really cheaply now. That would be best.
 
I would disregard BSW or BSF these were rendered obsolete mid late 50's. BSW and UNC share the same pitch but the former specifies 55* angle whilst the latter 60* so they will it together with one exception 5/8 or 11/16, I cant quite remember but the pitch is 1 out. The trouble you have is that the period of build , I would suggest is transitional between unified and metric. O/D and the pitch will be required to identify the actual form. ps you may find the nut is identified as unified by interllcked circles on a flat or an annular ring on the face, see net for illustrations
 
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Burnham Bob said:
My gooseneck is held on by a threaded metal piece that includes the rams horns and a captive shackle for the sail foot.

After removing the boom for a repair last season, I replaced it and tightened up the nut, and through the hole in the nut and threaded post stuck a split pin (the previous arrangement) to stop the nut working loose.

Wasn't quite tight enough - the shackle and rams horns revolved a bit under pressure. So this season I thought I'd use a nyloc nut and tighten up hard without bothering where the hole was.

Trouble is when I went to get a nyloc nut the thread isn't a normal thread available these days. So, its a Kemp mast and boom on a 1978 boat - what thread do forumites think it might be? It's a 3.8ths something or other....... individual imperial nyloc nuts are pennies on ebay so I don't mind ordering a few.
Click to expand...



If You have a nut that fits why not put some Loctite on the thread and tighten it fully?
 
agree - probably loctite! mind you it may be that a extra half turn will tighten the assembly and still leave enough room for a split pin to go through the hole
:)
 
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third engines said:
I would disregard BSW or BSF these were rendered obsolete mid late 50's. BSW and UNC share the same pitch but the former specifies 55* angle whilst the latter 60* so they will it together with one exception 5/8 or 11/16, I cant quite remember but the pitch is 1 out. The trouble you have is that the period of build , I would suggest is transitional between unified and metric. O/D and the pitch will be required to identify the actual form. ps you may find the nut is identified as unified by interllcked circles on a flat or an annular ring on the face, see net for illustrations
Click to expand...

I beg to disagree, I started work as an apprentice with the National Coal Board in 1963 and we were still using BSW/BSF then. My NCB supplied tool kit was the same!
Stu
 
VicS said:
Meccano ?
Click to expand...

5/32" BSW, apparently (so at least one British institution survives French and later Japanese ownership*).

NorthUp said:
camera tripod mount.
Click to expand...

I think that may be right but suspect the same question asked in the US would be answered with 1/4" UNC rather than BSW.

Edit: just done a little more rooting. Tripod threads evidently come under ISO 1222:2010, which specifies UNC of various sizes, but 1/4" for normal SLR mounts. This may have its origins in much older Royal Photographic Society recommendations of 3/16, 1/4 and 3/8 inch BSW. All are of course very close to their UNC equivalent.

* And Meccano, I see, became Canadian in 2013.

Apologies to Burnham Bob for...er, thread drift.
 
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