7/8"bsf. A die nut will be expensive particularly if it is LH thread. You can get a British standard thread file relatively cheaply or obtain a 7/8" bsf wheelnut with the larger 1 15/16" AF head and cut angled slots across the threads in three places and thus make your own die nut.
Alternatively remove the stud and take it to an engineering machine shop for repair if the threads are not too bad.
.

A few years ago I found out just how powerful these Sealey ones can be. A well know major restorer and body shop had refitted the front wheels to a bus without noticing that the stud holes were oval. Not content with that and incidentally fitting the brake camshafts on the wrong side of the vehicle, they proceded to overtighten the wheelnuts. It needed a lot of effort to turn the torque multiplier handle, enough in fact to worry me that the gear casing might explode. Each nut came undone with a load bang, but three were particularly loud and violent.

Having removed the nuts I found that three had sheared at the junction of the hexagon and the cone. This left the wheels still held firmly in place by the remaining thread within the cone. The wear and ovality of the stud hole had allowed the cone of the nuts to jam.

Is that the bus that was down my old place? I remember it well.

My bus number (if any): RML2532

My bus number (if any): RTL 960, RMC 1458, RM 1585 and several RTs

Yes it was the same bus.

I haven't the foggiest idea how they tightened the wheelnuts, all I know is that they were too tight. A 1" burp gun wouldn't undo them so I resorted to a torque multiplier.

The expensive Norbar multipliers which have a 1/2" or 3/4" square drive input are meant to be used for tightening. One just inputs force with a torque wrench set to the correct division factor. So a 4:1 multiplier would need the torque wrench set to 250 lbft to achieve 1000 lbft output torque.

I won't mention the occasions when one could use a Sealey type wind up multiplier sensibly for tightening, because of the possibility of a future reader attempting to use internet crystal-ball-advice about a problem, as professional instructions for which the writer should be held legally accountable in their misguided opinion.

When I went to Narbonne to help with the pick up of RM 48, the experienced driver tried everything possible to try and undo the front wheel nuts, we even checked the threads to see if some berk had put the wrong studs in and we were trying to tighten them!
In the end we had to take the tyres off!
Rob Duker will testify to how tight they were as he couldn't shift them nor a professional tyre fitting firm either, must have been a very powerful air gun to tighten them up, or four blokes leaning on a 10ft pole :)

My bus number (if any): RTL 960, RMC 1458, RM 1585 and several RTs

Hi Roy
Thanks for the info on the thread size, I got a die nut for the RH thread and got of by dressing the LH .
Regards
Iain

My bus number (if any): RM1807