Whitworth tank bolts ?

[PeteL]

My 1952 VH500 has petrol tank bolts 5/16" X 18tpi.
To me this seems to be a BSW thread, which seems odd.
The bike has not been used since 1960 and has very very few signs of being "messed about with" and it does not look like a bodge.
I checked Drags lists but actual thread type isn't mentioned and a search on here didn't reveal much either.
I discovered that Ariel later went to UNF & UNC but surely its to early for the threads to be UNC
I realise that 5/16" BSW is right and I've nothing to worry about. Just want to be sure.
Looking at getting slightly longer bolts to give the choke and throttle cables an easier route under the tank.

[dave.owen]

Whitworth bolts are correct for the tank.they are shouldered bolts to prevent over tightening puncturing the tank.

Dave

[simon.holyfield]

I thought it was odd as well - cei is the obvious choice, but all my Ariels (apart from the FH) are the same. Just make sure you wire lock them.

[PeteL]

Thanks guys That's a big help.
I know about the puncturing tanks. Did it on my 1st bike, back in '69.

[paul.jameson]

The petrol tank experiences quite a lot of vibration, which is why it is rubber mounted. CEI thread would be the natural choice for the bolts but the thread depth of CEI is very much less than that of Whitworth which might explain why Whitworth is used.

[nevhunter]

It's one of the issues I've had over the years. Now a days I make each bolt to fit tightly to avoid further thread damage. Lockwiring will help. Sometimes to get the tank to sit right I have to vary the top rubber(s) thickness. Nev

[MGriffin]

I made up and fitted studs with locknuts