I have an old "Hero" type Derringer with this nipple fitted:http://s133.photobucket.com/user/mag...tml?sort=3&o=0

The flats seem closest to a 4BA spanner, OD of threads is .2215", I don’t recognise the thread but it looks a little course.

Is this a standard size nipple, and if so, does anyone have any spare ones, or know where I can buy a couple?

Do your nipples suffer with use and need renewing?