I think this is an original 14HP Crossley radiator cap, although I could be wrong.The thread diameter is 1-7/8" with a 20TPI.It's not perfect, however, it will come up well with a bit of work. The nickel will polish up OK. There has been a bolt put through the middle and would be better off replaced.Othe..
Wilmot Calormeter in fair condition for its age, have placed in hot water and it still works, £100 plus P+P for more details call Tony 07951 819786 Warwickshire.