Starter switch

**peterg1001** · 20th June 2010, 02:52 PM

Does anybody know what the thread is on the copper bolts at the rear of the starter switch?

It's close to a 5/16", but it's not UNF or UNC. Most likely Whitworth?

Thanks, Peter.

**Aaron IIA** · 21st June 2010, 06:48 PM

It is most likely BSW. My question is though, how have you been able to distinguish between UNC and BSW? Did you accurately measure the thread angle? They both have the same TPI.

Aaron.

**peterg1001** · 21st June 2010, 08:28 PM

Distinguishing between the two is based on the purely empirical observation that the nut off the back of the switch won't screw onto either a UNF or UNC bolt.

I'll try a UNC nut onto the switch, and see if it fits.

Otherwise, I'll get some BSW nuts and try them.

Alternatively, I could just leave the original nuts in place, but that's not much of a challenge, is it?

Peter

**JDNSW** · 22nd June 2010, 05:43 AM

I don't know what it is, but the most likely is either BSF or BA if it is not Whitworth. Very unlikely to be UNC, although as commented - this is, for practical purposes, indistinguishable from Whitworth in that size. It is even conceivably metric, although worth noting that BA is a metric thread, with a different threadform to ISO metric.

John

**peterg1001** · 22nd June 2010, 11:51 AM

Thanks John. I've had another try, and a 5/16 UNF goes on about 1 turn then stops. I'll go with 5/16 BSF, seeing UNF and BSF are 24/22 threads respectively.

I've ordered some nice brass nuts from Classic Fasteners, so I'll see how they go.

Peter