Hi
I bought one of the SRM hex ones, when putting my A-10 together.
But it simply wouldn't fit - no way I could get it to go on the tread - so I had to reuse the old nut, that went on with no problem...
Wrote SRM about it, and we agreed to return it and I got a full refund.
A mate had made up an old socket with 4 wings that fit the old C-spanner nut, worked well.
regards
Joergen