C4 vac tube size?

[Torkman66]

Making s new metal vacuum line from manifold to C4 modulator. Can someone tell me what size metal tube should be used? I think it may be 3/16 but that is brake line size and seems a bit small. I know rubber vac lines connect tube at each end.

 

[Glass Pony]

Mine is 1/4".

 

[Ol'Blue]

Mine is 3/16" ID 1/4" OD

 

[Torkman66]

Thanks guys.

 

[Oldtimer]

I know C4s are old technology, but really, vacuum tubes?