[Aussie Mike]

I think the convention 4 on16 is right but a lot of the hose specs I see have an actual inside diameter smaller than than 1/4" or 1/2" etc.

Any idea why? Is it based on the need for a tight fit over a standard size barb?

I've bought SpeedFlow, Russell and Earls in the past and they are all smaller than the nominated size. Russel for example quote 7/32" ID for their 1/4" #4 line.

Cheers