Clutch slave cylinder mounting bolt threads

[Webley1991]

Am I correct that the bolts used for mounting the clutch slave cylinder to the bellhousing should be 5/16" Whitworth. This is on a '72 Series 3. I remember reading that everything on the series gearbox was Whitworth.

Unfortunately I have mislaid the bolts afer stripping the vehicle down. I don't want to force a Whitworth tap into aluminium without knowing for sure.

Thanks for any info.

 

[jamesmartin]

5/16 unc

 

[Webley1991]

I managed to find the ones I took out and I see that they are BSW as the crests and root of the thread are rounded.

Do you have any drawings showing that it should be UNC?

I would like to be fully certain that I am using the correct thread, as they do get put under a fair amount of force. They are also in a soft material.

EDIT: I found some bolt identification info online. If a bolt with no number grade marking has a circular indent in the centre of the head, it can be assumed to be UNC. The bolts I removed do have the marking, so UNC it is. Now it begs the question why they would use UNC when everything else on the box is Whitworth.