[Dan Case]

Cobras, 427 Cobras, and 289 Sports all use the same center lock nut thread "size". The average I have measured on a collection of used and new old stock hubs covering all three chassis types is a minor diameter around 2.17" and a major diameter around 2.332" and threads cut at a 55° angle.

Halibrand Engineering supplied three wing center lock "knock off" nuts in forged and heat treated steel and aluminum versions for new 427 Cobras that were stamped "55" presumably to notify mechanics were type threads, by angle of cut, the hubs and or nuts had.