Doc, I'd try these. They're all metal, so even though thin, the locking part is still a viable part of the nut. Nylocs can end up with next to no thread if thin and sporting a heavy chamfer on the non locking end.
https://www.ebay.co.uk/itm/1-4-5-16-...HCqRYt4mNAwoVQ
If too thick, they could be skimmed down on a lathe.
£2.20 for 10. enough to do all 4 corners.
Mart.