Further to the above - nut arrived safely and I set about installing it. At the point where I was installing the low B the nut snapped - suggesting that the .120 was too large for the nut. I was hoping to replace with a metal nut - Got in touch with Mark and John - a 42x6x6.5mm nut in metal does not exist apparently - John felt sanding a 45mm black one would be unsightly - new nut in the post - no charge.
This time I've gone to the trouble of running some sandpaper through each of the grooves to allow for some additional space.
I'm not 100% sure that the payment is secure even at this point. Lots of scams that could be used for scammers to get the bass and their cash back.
Be careful.