K
Can't work out how that lock ring operates though. If it's the steel ring then no problems but if it's just that brass ring above the button I reckon that could be a right PITA (with it being the saem diameter and thin).
https://www.flickr.com/photos/102856770@N03/12848117105/in/set-72157640897891165
It looks like something I would easily break!