Anorak time; bolt size

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abowie
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#1 Anorak time; bolt size

Post by abowie » Sat Oct 14, 2017 6:27 am

I've been trying to work out what thread the bolts holding the bell housing to the Moss box are.

The head is best fitted by a 3/8 W socket.

The bolt is 18 tpi and matches my 5/16 W thread gauge perfectly BUT it's 0.406" (13/32) in diameter, not 5/16.

I've exhausted my patience with internet searching.
Andrew.
881824, 1E21538. 889457. 1961 4.3l Mk2. 1975 XJS. 1962 MGB
http://www.projectetype.com/index.php/the-blog.html
Adelaide, Australia

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265bhp
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#2 Re: Anorak time; bolt size

Post by 265bhp » Sat Oct 14, 2017 11:48 am

Not sure if this will help Andrew...but they are listed as FB. 107/13D in the parts catalogue....and C9859 / C9860
Regards
Jonathan
1963 3.8 FHC ..now finished …………….
1974 2.7 Carrera now as an RS Touring

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#3 Re: Anorak time; bolt size

Post by abowie » Sat Oct 14, 2017 9:17 pm

265bhp wrote:Not sure if this will help Andrew...but they are listed as FB. 107/13D in the parts catalogue....and C9859 / C9860
Regards
Jonathan
Yes, I found that. All NLA and I can't decipher all of the long bolt code.

F = Fine thread
B = Bolt
1= Hex head
07 is not a valid diameter code for a bolt
13 = 1 5/8" length which is right
D not a valid code position

I have all the bolts I need but I'm interested to know what thread it is...
Andrew.
881824, 1E21538. 889457. 1961 4.3l Mk2. 1975 XJS. 1962 MGB
http://www.projectetype.com/index.php/the-blog.html
Adelaide, Australia

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Hugo
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#4 Re: Anorak time; bolt size

Post by Hugo » Wed Oct 18, 2017 3:34 pm

Couldn't be a Helicoil thread I suppose?
As I'm sure you know, most BSW threads are the same pitch as UNC (although the profile is slightly different).
You say a 3/8" BSW wrench fits the head. That's actually a bit ambiguous - originally a 3/8" WW spanner size was the same as a 7/16" BSF, and many wrenches had dual markings. Whitworth nuts & bolts had bigger heads than their BSF counterparts. In the old days, any time you heard a mechanic asking for a "quarter Whit" spanner, you can be pretty sure what he really wanted was a 5/16" BSF, although that is academic as they're the same size.
Then, during WWII I think it was, they reduced the size of the heads on WW nuts & bolts to make them the same as BSF in order to save metal.
The size across flats on both BSF and WW is some weird fraction - no idea where they got it from.
But to get back to your bolts, if it's any consolation I haven't a clue either, other than my original suggestion.
Hugo Miller - rebuilding an imported Series II OTS & converting to RHD

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