I've got the bolt and I'm trying to source a tap but I'm unsure if it's 3/8 bsf or m11.....

measuring with a pair of cheap digital calipers;

thread od = 10.95mm
10 threads = 12.6mm

I can't get the jaws of the calipers properly inside the thread to measure the inner diameter but at best I recon it's 9.8mm

AF = 15.6mm



any ideas....

Give us a clue of age of the bolt. Or a picture of the end.
What is marked on it?

Sounds like 7/16 UNF, its too large dia for 3/8, if it were M11, the pitch would be 1mm 1.25mm 1.5mm depending on fine coarse etc....

[Edited on 12/12/14 by r1_pete]

7/16th s UNF?

That's definitely and imperial bolt.

Metric bolts would have a grade mark like 8.8 or 10.9

I would say 7/16 UNF too

http://www.unionmillwright.com/2879.pdf

0.4375 x 25.4 = 11.1125mm

UNF would be 20 threads per inch

Here's a BSF chart too
http://www.motalia.com/Html/Charts/bsf_chart.html

[Edited on 12/12/14 by DW100]

Cheers guys

Are you in a rush, I'm 99% sure I have a set of 7/16 unf taps, I deffo have 3/8 and 1/2, if you can wait so I can check later, you're welcome to a loan, decent taps aren't cheap....
I'm at J31 M1....

7/16 UNF is the size on seatbelt bolts I believe?

Thank you for your kind offer R1-Pete. I've put a call into my dad this morning and he's certain he has one....but failing that I may take you up on your offer