thread size please

[stuffedpike20]

Does anyone know the thread size for the tube nut that holds the pipe to the petrol tank please? Does not seem to be on the list at the top of this topic.
Is it 1/2"BSP ?
Thanks.

[pgp001]

It is unlikely to be 1/2" BSP that would be approx 0.825" across the threads.
I would expect it to be more likely 1/4" BSP which is 0.518" dia.

Hope my answer was more helpful this time.

Phil P

[stuffedpike20]

I measured the O/D of the threads at 1/2", and assumed BSP as it is a pipe fitting.
Am I wrong?

[philthehill]

The thread is 1/4" BSP x 19 TPI. The tapping drill is 11.80mm.
If you drill to 10.50 mm you may be able wind out the remains of the old union.
1/4" BSP equates to near 1/2" O.D.

[stuffedpike20]

Thank you.
Do you measure the diam of the hole on a tube nut to get the size then?
I am ignorant of such things!

[pgp001]

Yes it is the nominal bore of the pipe used for BSP.
Quite often the thread is applied directly to the ends of steel tubing so that is why it is done like that.

You are not the first person to misunderstand this, it catches plenty of folks out.
I am a mechanical design engineer by trade, and have whole books dedicated to just screw threads, it is a bit of a minefield.

Phil

[stuffedpike20]

Thanks Phil.
As the kids say nowadays, 'every day is a school day'!