Head stud carb confusion

Ready to mount my JS Motorsports twin carbs and the studs do not fit the head. I bought them from Old Britts and they are the correct part for the 1974 Norton Mk 2.

# 060577 Stud, 5/16 x 24, Carb

The problem is that the hole in the head is a 18 TPI, not a 24 TPI. I searched the Old Britts catalog for different year studs and they all seem to be 24 TPI.

What gives? Now finding some 1 inch, 5/16 x 18 automotive studs is turning into a chore. (McMaster-Carr comes to mind.) Any help or suggestions?

Thanks in advance.

*18 TPI bolt on left fits cyl head holes perfect, the Old Britts part on right does not.

I think you need to know that the studs that you have go into the Amal mounting manifolds and not the head. 5/16 -18 allen/hex head bolts go into the head and is what you need to mount JS's manifolds or the standard mainifold to the head.
See part number 6 and 7 is what you need, not number 3.

http://www.oldbritts.com/1973_g12.html

All I can say is welcome to Norton, UNC in thaqt location, but Cycle or BSF for the allen head screws at the head steady mount, so switch those boys around and you can have some fun.

Cheers Richard

It is my impression that the manifold to head Allen bolts are 5/16-18 BSW, but I kludged it and put in 5/16-18 UNC.

Dave
69S

According to a website which compares the two:

"1/4BSW and 1/4UNC threaded fasteners are interchangeable, as are 5/16BSW and 5/16UNC threaded fasteners."

Others as well, only 1/2 isn't. Hardly my area of expertise however.

VintAge said:

According to a website which compares the two:

"1/4BSW and 1/4UNC threaded fasteners are interchangeable, as are 5/16BSW and 5/16UNC threaded fasteners."

Others as well, only 1/2 isn't.

Click to expand...

Only "interchangeable" if a person isn't bothered about the difference between 55 degree Whitworth and 60 degree Unified thread angles! :shock:

http://www.britishfasteners.com/threads/bsw.html

http://www.britishfasteners.com/threads/unc.html