Rear Diff

I have just bought a rear diff guard and it bolts onto the bottom of the diff, does anybody know what thread the two holes are? i haven't got a thread gauge small enough to get into the holes :/

whitworth ,bsc

Something quite old. 3/8" BSF im pretty sure, I have a tap which I cleaned mine up with, just can't remember for sure without looking!

Thanks its a whitworth and its a 5/16 thread.
Cheers for the replies and help

BSF or BSC? just curious to know whether i remebered correctly...

cheers anyway

bsf you were right ,its a bolt i allways save when stripping diff even though dont send diffs with them

yeah luckily my qt diff guards came with bolts, otherwise i would have been fairly snookered.

luckily my dad had a bsf tap set in his old tool box, i needed to tap out the holes to clean them up and a new one was rather dear!!

Just to clear this up, they're 3/8" BSF.

Now there's a coincidence....I was under m bobtail RRC yesterday wondering what the options are in terms of mounting the front QT guard I got, when it already has a Gwyn Lewis steering rod guard on....
I had thought about modifying the mount, so both guards use the same two bolts to hold them on the base of the diff..so I would've needed longer bolts to do that job.....and was about to look see what threads they are.
However, after further thought have decided not to go down that route, instead gonna mod the QT unit to weld on to the rod guard