After 40 years of production even the British have made some improvements; this is one of them. The current production cylinder head nuts have a built in flange to spread the load and improve clamping force. They may be used on any A-Series engine. And please note- head nuts do have a finite life- they will not work forever just because you have not lost them does not mean you should not replace them. Not only does repeated on and off application degrade the threads but extended time under compression load can also effect their capabilities. Also fits a Sprite , and MG Midget .