I wanted the overall length to be 22mm. There is another seller who has the dimension on for the different valves. The 8mm one you pictured has the length at 21.5mm.
I have bought a CF bottle for my Priest, and the priest valve that is fitted as standard is a different thread (not 18x1.5). I've bought a new reg assembley, but the valve protrudes too far to allow the bottle to screw on, hence the search for a shorter unit. At the very worst I can remove the valve from my other bottle, but at the moment I'd prefer not to.
Rob