Lucas RB108 nut size

[bl**dydrivers]

Hi all
It’s been awhile since my last post

However I’ve lost the nuts that secure the Lucas Voltage Regulator to the toolbox and can’t find any information to the size of the nuts.

My Whitworth thread gauge says it’s 24 tpi and it’s about 1/4” but can’t find any nuts matching that and only find nuts 1/4x26

[trevinoz]

I am fairly sure that they are 1/4 BSF, will check later. 1/4 x 24 is common on Harleys.

[limeyrob]

They are a nut and bolt so you could swap both:
nut - 02-2395
bolt - 02 - 1354
washer - 25-7180

If you search BSA 02-2395 it comes up as 1/4 BSF (26 tpi).

[bl**dydrivers]

They are a nut and bolt so you could swap both:
nut - 02-2395
bolt - 02 - 1354
washer - 25-7180

If you search BSA 02-2395 it comes up as 1/4 BSF (26 tpi).

It’s the later type with the rubber molded around the studs with a square to fit onto the toolbox brackets.

I’d have to check to see if I have any spare 1/4x26 nuts

[trevinoz]

In fact they are 5/16 x 24 tpi which is 5/16 UNF. 1/2 AF.
The nut is 3/16 thick.

[limeyrob]

OK not the bolts through the back but the nuts on the ends.  Lucas went metric and UNF before most other UK manufacturers so their threads can be a real gamble.  5/16 x 24 UNF is my bet too.  The nut is not listed as it comes with the regulator.

[Rex]

If it's ended up with a Unified thread then my guess would be that it's been changed.
BSA pre-unit twins were made too early to have suffered the Imperial/Unified changeover.

[trevinoz]

The nuts haven't been changed, they are original on a 1961 RB108 regulator that I have spare. It would be difficult to change the nuts as the studs are bonded to rubber mounts and attempting to re-cut the threads would be asking for trouble.
If they had been re-cut it would be evident.
I have two RB108 in that style on bikes and I am sure that they have the same as I described.

[bl**dydrivers]

Went to Home Depot (US version of Home Base) with the regulator to use their thread checker and think it is 5/16x24.
Reason why I say think is because I couldn’t screw it in all the way as someone drove a screw 1/2 way into it.
I’d have to order some stainless ones from Amazon as Home Depot only had a box of 50 zinc.

Thank you all for your responses!

[Rex]

The nuts haven't been changed, they are original on a 1961 RB108 regulator that I have spare.

Just a thought; wasn't the RB108 used on some British cars when the old electromechanical regulators were being phased out, and didn't the car industry change to Unified threads late 1950s/early 1960s?

[Swarfcut]

  They sure did Rex, and all was fine until the introduction of  Metric Threads as a European standard. To confuse even more, there was a short time when what looked like AF nuts and bolts came with metric threads as British industry moved away from the old UNF and UNC fastenings.

 This meant your old AF spanners still fitted, but an AF bolt from your big rusty tin didn't. Ford gearboxes were an example I remember, meaning the local spannerman did not need to invest straight away in a complete set of metric sockets, and neither did the factory.

 Swarfy.

[limeyrob]

Agreed, Lucas especially were moving to UNF and Metric (at the same time it seems!) and so were Smiths.  The speedo cable threads are metric.  BSA were happy to use a combination of metric and imperial bearings in the hubs from the mid 50s.

[bl**dydrivers]

Ordered nuts from Amazon, taking forever to come, so went through all my spare nuts and found a couple of stainless half/jam nuts that fit.
Presume they’re 5/16x24

[Rex]

They weren't a great reg when they were new, let alone now.
I'd gut it and fit a DVR2 if I were you.

[bl**dydrivers]

They weren't a great reg when they were new, let alone now.
I'd gut it and fit a DVR2 if I were you.

Already have one but need the courage to open the box without breaking anything and wondering how to mount it inside. 😉