Fitted some new axle nuts to the Brompton. This took three hours.
The dropout design has changed over the years, and the new SRAM anti-rotation washers expect the little slot above the actual dropout to be closer to the open end of the dropout. I had to very carefully make the little slot deeper so the washers would engage, using a small file. When I just managed the snuggest of snug fits (which is how it is on my S-type) I stopped.
Then I found that, although the axle nuts are correct, the guide nut is a Sturmey one
I'll have to e-mail the shop, since they all came in the same bag. SRAM use a weird German FG10.5 thread (10.5mm diameter and 26TPI) but Sturmey use a 13/32" x 26 TPI thread. The difference in diameter is less than 0.2mm and the pitch is the same, but they'[re not interchangeable. Anyway, I can tell it's a Sturmey nut because it has a porthole in it - SRAM ones don't, because you don't need to see the end of the axle to adjust 'em.