If my memory serves me correctly, it is 5/8. The issue is that for one of them, coming off the pipe on a 302, is 3/4. I once posted a Goodyear part number that was a length of straight hose 5/8 on one end and 3/4 on the other.
But, any good parts counter man should know what you need. You could also try doing a search, you might find my old posting. I think I did it in 2003.
A forum community dedicated to Factory Five owners and enthusiasts. Come join the discussion about performance, racing, conversions, modifications, troubleshooting and drivetrain. We discuss MK4, GTM, 818, Type 65 coupe, roadsters, and more!