I am using stock MX5/Miata brake and clutch pedals and life is so much easier of I can use the master cylinders too. I have 3/8" brake line and nuts in stock already and I want to use the Wilwood proportioning valve which has 3/8-24 ports:

http://www.speedwaymotors.com/Wilwood-Adjustable-Proportioning-Block,41747.html

Will metric brake line nuts work on 3/16" brake line?

I am guessing they will as the seal is on the flare not the brake line nuts, but I wanted to check. If they will it'll help with the conversion at the master cylinder, it makes my whole plan so much easier because AN3 and 3/8-24 fittings and 3/16" line are available everywhere and the layout keeps down the number of fittings and adapters.

-Steve

Yes. Brake pipe (line) here in UK is all 3/16" whether the nut is metric or imperial.

Brake pipe is exactly the same, but US cars use SAE style flares Metric cars use DIN style flares. It usually dosen't matter too much if you use the wrong type provided you make nice fat flares.

Thanks ... That sounds simple then, just make the right flare on the end of the pipe and it's good.

-Steve