Enfield nipple thread

[gmkmd]

Anybody know the correct thread size on an original Enfield nipple?

[Blair]

The closest "U S modern equivalent" is 5/16-18. This is based off of a 60 degree thread pitch.
Where as the British Whitworth thread of the period is very similar, it is based off of a 55 degree thread pitch.
I hope you find this helpful,
Blair