I have a saab concentric slave i need to pipe up,what size pipe is best to use 1/4 or 3/16 copper . The master cylinder i am going to use has a 3/16 pipe outlet.

OEM use 1/4" but In practice it doesn't matter 3/16" is much easier to use.

Thanks for that i have some 3/16 pipe and fittings.

I used 3/16 on my saab cylinder and all is well