I've ordered the special nutbush from Fowlers in Bristol, they're on back order. I've bought a 30mm long M10 threaded insert bush. 22mm diameter as I didn't have a plan.
Now I do, I'm going to turn it to match the nutbush. Then lock it in place with a locknut.
I may in the future buy larger diam and have a 24mm nut head, for now flats will suffice.
It's a temp measure until my order arrives. Ha, they all say that !