Stud Thread size

[ramwing7]

I have a 1963 Norton Electra.
One of the breaker point pillar stud bolts has broken off.
I've extracted the remains, refilled the hole, and ordered new studs.

Thing I need to know is the size tap I should use to rethread the hole.

Anybody know that?

Many thanks.

[L.A.B.]

Points assembly pillar bolts are usually 2BA but I can't find a part number for them so what is the diameter and TPI?

[iansoady]

He'll struggle to meaure the tpi of a BA thread with a conventional thread gauge..... However, meauring the major diameter (in mm) should give the BA size. 2BA would be 4.7mm and 1.234568 threads /mm. 3/16" BSW is a similar diameter but 24 tpi.

[Rex]

I can't think they'd use a Whit thread here, but can't you check the remaining stud with a 2BA nut?

[ramwing7]

Thanks.

My kanoodling got me to 5mm, so I must be in the ballpark.

[R]

How different are these to Commando ones - which are 2BA
And a shade over an inch long - overall.

btw, a 5mm nut will thread onto these - as a rather loose fit.

[Rex]

It may wind on, but I'd never describe it as any sort of "fit".
Rather like OBA and M6, slack as something very slack, although there have been claims of interchangeability by some...

[R]

BA is a metric-based thread system.
Only the English could take that and mangle it just enough to call their own !?

It may not be any sort of 'fit' at all, but the 5mm going on at all means you can test what it may be.

[Rex]

Given that BA stands for "British Association" I take it that you really mean British rather than English? That said, and given that it was a thread based on metric units, it wasn't "mangled" from anything else.
One of the most useful of the small threadforms, and far better than the metric series or the dreadful Unified small sizes.

[R]

Hmmmmmm ?

[33d6]

Give over you two. We all know it's 2BA. It's British electrical, what else is it going to be?
I like the BA thread. It's a practical thread form that makes for a much sturdier screw than comparitive sizes in other formats. The 47.5 degree form gives you a greater core diameter than the common 55/60 degree forms used by metric, US and Whitworth. Its a format designed for fine work in small diameters and it does it well. Yes, it's day is mostly done because electronic instrumentation and the microchip has taken over much of the old mechanical instruments of yore that it was intended for but that doesn't alter it's effectiveness.

Having a background of nutters who played with this stuff before I was a twinkle in my father's eye I now have the family accumulation of BA, Whitworth and SAE taps, dies and some ISO metric God Wot. BA is by far the sanest for small stuff. Just don't get me started on small ISO Metric.



 

 

[iansoady]

I agree that BA is a very logical thread series. Its only drawback for me is that it can't (at least not with any facility) be screwcut in the lathe which is what I prefer for male threads.

[Rex]

Treat yourself (if you haven't already got one) to a tailstock die holder if you need to cut a BA thread on a lathe. Life really is too short to screwcut a BA thread on a lathe though..

[DM]

Even better is to get yourself a coventry die head.

[Rex]

Yeah, if you're made of money...
Hardly justifiable for the use-it-now-and-again amateur.