Identifying stainless steel bolts.

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Dan Tribe

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I've found a bit of crevice corrosion on a chain plate bolt so have decided to replace them all.
The old ones have SN - JH A2 marked on the head. I assume the A2 refers to the grade but is SN - J2 significant? Tried Google but can't find anything that I can understand.
The old bolts were actuall machine screws, I understand part threaded bolts are preferable?
Any comments please?
 
Dan Tribe said:
I've found a bit of crevice corrosion on a chain plate bolt so have decided to replace them all.
The old ones have SN - JH A2 marked on the head. I assume the A2 refers to the grade but is SN - J2 significant? Tried Google but can't find anything that I can understand.
The old bolts were actuall machine screws, I understand part threaded bolts are preferable?
Any comments please?
Click to expand...

Bolts usually have hexagonal heads and are only partially threaded . The fully threaded ones are "set screws"

Machine screws are the ones that have countersunk heads, pan heads , cheese heads.or raised heads..... not seen machine screws with any head markings

A4 (or 316) would be preferable to A2 / 304

AFAIK SN-JH is the makers mark


Look at Seascrew and A2A4 fixings websites

https://www.seascrew.com/browse.cfm?ONLINE-CATALOGUE&l=TOP

http://a2a4.com/

When you fit the new ones be sure to seal the bolts/ screws well in the holes so as not to leave any crevice into which sea water can penetrate
 
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VicS said:
Bolts usually have hexagonal heads and are only partially threaded . The fully threaded ones are "set screws"

Machine screws are the ones that have countersunk heads, pan heads , cheese heads.or raised heads..... not seen machine screws with any head markings

A4 (or 316) would be preferable to A2 / 304

AFAIK SN-JH is the makers mark


Look at Seascrew and A2A4 fixings websites

https://www.seascrew.com/browse.cfm?ONLINE-CATALOGUE&l=TOP

http://a2a4.com/

When you fit the new ones be sure to seal the bolts/ screws well in the holes so as not to leave any crevice into which sea water can penetrate
Click to expand...

Thanks for the clarification VicS.
They are hex head fully threaded set screws then, I'll try to remember the proper name..
Another little anomaly is that they seem to be 9.37 mm dia which doesn't seem to fit any metric or imperial size. The head takes a 15mm socket , which seems odd.
I've had stuff from Kays Fasteners before, they seem reliable but will try Sea- Screw,
Thanks for the info.
 
Dan Tribe said:
Thanks for the clarification VicS.
They are hex head fully threaded set screws then, I'll try to remember the proper name..
Another little anomaly is that they seem to be 9.37 mm dia which doesn't seem to fit any metric or imperial size. The head takes a 15mm socket , which seems odd.
I've had stuff from Kays Fasteners before, they seem reliable but will try Sea- Screw,
Thanks for the info.
Click to expand...
They will be 3/8" Whitworth then. assuming they are 16tpi
 
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TQA said:
Crikey Whitworth ? I thought that had died out and everything was UNC nowadays.
Click to expand...


Almost entirely metric in the UK

Whitworth was still common until around late 1970s. All the original bolts and screws on my boat are Whitworth

UNC/UNF was used in the automotive industry until superseded by metric ( Whitworth in the distant past before my time but long gone, like the man with a red flag)

I believe one or two dinosaur nations still use UNC/ UNF along with other, sometimes corrupted, Imperial units of measure such as feet, pounds , gallons etc
 
skipper_stu said:
iirc correctly the 15mm socket fits the old 5/8” AF headed bolt
Click to expand...

It is a very snug fit on a 3/8" Whitworth bolt.
5/8"AF is a bit bigger so I didnt think 15mm would fit on it but I cannot find one to try. Very sloppy though on a 9/16" AF head. (Found a couple that size on the Evinrude)
Anyway 5/8" AF head would correspond to a 7/16" bolt not 3/8" which would have a 9/16" AF head


Useful table of spanner jaw sizes at https://www.sat.dundee.ac.uk/psc/spanner_jaw.html


Also a bit of history on BSW / BSF head sizes which mystify most people who come across them!
 
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VicS said:
I believe one or two dinosaur nations still use UNC/ UNF along with other, sometimes corrupted, Imperial units of measure such as feet, pounds , gallons etc
Click to expand...

The gallon of which you write was corrupted, if it was corrupted at all, by a dinosaur on this side of The Pond. It began life as the Queen Anne gallon, a measure once favoured in the UK for bulk wine. This gives it, in my view, a certain sanctity. Until relatively recently, wine and spirit bottles, in both the US and UK, were commonly one fifth of a Q. Anne gallon. (Hence the colloquial US description of "a fifth" of, say, bourbon.)

Squaring the circle, I see there's now a Whitworth gin...
 
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Thanks everybody, it sort of makes sense now, my UFO is a 1970s built boat. Great expertise here. I used to know some of this stuff but never really got to grips with the various changes in bolt and thread types. To think that some people want to go back to pre-metrication days!
 
Dan Tribe said:
Thanks everybody, it sort of makes sense now, my UFO is a 1970s built boat. Great expertise here. I used to know some of this stuff but never really got to grips with the various changes in bolt and thread types. To think that some people want to go back to pre-metrication days!
Click to expand...

A return to Imperial units, and shillings and pence, will be hidden deeply in the Brexit deal but we won't know about it until it's too late.
 
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If you look at any 'how to' American videos on YouTube, they rarely use metric measurements, preferring to say five sixty fourths and the like. Also they pronounce 'solder' as 'soda' which irritates me but that's another topic.
I was at university studying engineering when UK went metric which complicated my studies somewhat. "Bring back slugs, poundals, rods, poles and perches" is not a cry you'll hear me utter, metric is so much simpler thanks to Napoleon Bonaparte.
 
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