I think we have our answer. Sparkless fittings make sense.

I took a look at a Napoleonic fort sight in Plymouth UK for interest's sake. I'll have to go and see the disappearing gun now 'cos they used to have several on Flat Holm Island, just acroos the way, and I'd like to see what they really looked like.

Shame that one-roger hasn't come back with some links. I love this old tyme etymological archeology.

Thanks to all who've replied. You're a friendly and curious bunch. The only reply I got on an another (UK) site which should remain anonymous (BBC Radio 2 - Folk On 2) accused me of being needlessly pedantic. I thought I was just asking a question.

Erm . . . small point of physics but would the sparks from striking an iron nail with something be electro-static?