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MG MGB Technical - No 10 UNF

I recently saw a set of taps advertised. The sizes were No 10, 1/4", 5/16" and 3/8".
I understand the last 3 and could even tell you the AF sizes that go with them. However, I am unsure what No 10 is.
There are anumber of items fixed around the engine bay with small cross head machine screws that go into weld nuts. Are these No 10 UNF?
DJ Witham

Yes they are all 10UNF and that's about the only size of tapr you will need on the B
Iain MacKintosh

Iain is right about 10 UNF, but for all the cost of carbon steel taps and dies nowadays it's worthwhile having a small set for cleaning up threads.

Ron
R. Algie

A no. 10 machine screw is .190 in. diameter and comes in 32unf and 24unc thread pitch. Numbered screw sizes were standardized by the U.S., Britain, and Canada. Not sure where the numbered designation came from, but there is a formula to determine OD - screw number times 13 plus 60 gives overall diameter in thousandths (e.g., 10 X 13 = 130, then 130 + 60 = 190 or .190 in.).

Wayne
Wayne Pearson

Thanks for your help everyone.
David Witham

I always understood that the cross head screws were 2BA threads but there is so little diference that a 10 UNF would probably do!

10 UNF is 0.190 dia with 32 threads per inch.

2 BA is 0.185 dia with 31.4 threads per inch.
Chris at Octarine Services

You're absolutely right Chris and why we go to UNF for the 3/16 diameter screws I suppose we will never know. If you buy all the screws from say Namrick then it's al 10UNF they supply and they are fine.
Iain MacKIntosh

UNF and BA have different pitch angles, BA is 47.5 deg and UNF is 60, they are not interchangeable.
Ron
R. Algie

"UNF and BA have different pitch angle", This is true but a 10-32 and a 2BA are so close in pitch that they can be used interchangably. Prior to getting a 2BA tap, I used to clean the threads for the 2BA screws in fuel pumps with a 10-32 tap and had no problem at all. In fact, for a number of years, I repaired damaged threads in the fuel pumps with 10-32 helicoils regularly and it was impossible to tell the difference. I now have a 2 BA tap and 2BA recoils to repair the threads, just to keep things original. Anyone who would like a chart of standard threads that includes American, British and metric threads e-mail me and I'l send you the chart. Cheers - Dave
David DuBois

Interchanging 2BA & 10 UNF is bad basic engineering, they are different threads, different TPI, different diameters, different thread angle, you can also stick a self tapper down a 10 UNF hole but just because you can doesn't make it right.
Ron
R. Algie

Agreed Ron that it is not ideal practice but it doesn't really matter as the two are so close they even interchange opposite ways. Years ago we used to interchange the whole Whitworth range with UNC and vice versa all except 7/16 if I remember. The difference in the angle on these was 55 versus 60 degrees
Iain MacKintosh

This thread was discussed between 02/03/2006 and 03/03/2006

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