H1 SU versus Ruby Zenith sidedraft

[JonE]

The piston and aperture of the 1 and 11/8 are the same; the former may give a more progressive throttle action . The horizontal 1 1/8 with dashpot ex postwar Morris  is relatively common.

Thanks. I'm curious now as unsure what the 1" one is called if its not technically an H1, from John's point?
And what IS the difference between the 1 and the 1 1/8 if piston and aperture are same...? trying to get my head around where the extra flow comes in (or rather the potential for the flow hesitating, perhaps)