Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing 1973 Plus 8 aux Lucas long range lamp - lost the n

Hi, When removing the right side Lucas aux long range lamp on our 1973, I unfortunately lost the nut. And it has turned into a somewhat nightmare to locate a new one when living in a metric country, where very few knows about inches and British/American measurements. I measured the bolt to be approx. 11.12 mm thick and hence think its a 7/16". Now, I tried 7/16 UNF, BSF, differet metric nuts, but none of them seems to fit and UNC seems to be too coarse....Would be grateful for any advise to which nut I need and where I can get one. Pls see attached photo. Cheers Finn

Hi Finn, you are spot on with the thread diameter being 7/16 inch. Suggest trying a UNC or BSW nut of that size. They are virtually the same coarse thread with pitch of 14 threads per inch.

The 7/16 unf thread is used for all seat belt attachments, it remains to find a nut.

Hi, Sensei



UNF are 20tpi count the threads up say over 1/2" and double it. If you can ascertain that this is the correct size PM me and explain the type nut you want, I'll sort it for you and send them over. Just a thought, does the wires exit through the fitting stalk, Could be BSP?

Martin.

Sensei, bit more research and I have found a lucas (driving) mounting light nut part no. 632A it is brass and 7/16" and classed fine thread having 26tpi they are the princely sum of £8.20 each and are retailed by SVC Stafford Vehicle Components. Hope that helps!

Thread form is actually an obscure thread being 7/16" BSB.

BSB is British Standard Brass which is a 26 tpi Whitworth thread form (55 degree thread angle) as opposed to the 60 degree thread angle found on BSC/CEI threads.

As luck would have it I am making a batch of these nuts tomorrow night as they also fit the side lights on my 1955 Plus 4 DHC.

So rather than pay the frankly ridiculous sum of £8.20, I'll make you one and post it to you!

PM me your address and I will get one out to you.

Arwyn

Nice one Arwyn!

Interesting bits of trivia. The 7/16" BSB thread diameter doesn't appear to exist in online thread tables making them more rare still. Second, the pitch is fixed at 26 tpi across the thread diameter range. This because it was originally proposed for brass tubing which itself has a nominal equal thickness across the size range, hence need to fix and limit thread depth with fixed pitch so as not to reduce threaded tube integrity.

Excellent Arwyn, Yep £8.20 is a fortune for a brass nut! Somewhere we have the taps but I couldn't find them today, even looked through my late dad's stuff but not found them yet. As far as I remember there are no die's, you have to turn it on the lathe or a thread cutting machine.

Found a 1" die from a thread cutting machine! It's marked BSB but labelled british brass thread. it has 5 cutting sections, guess for stability on thin walled pipe.