It's going to be stored inside a tube that diameter, so button function is not so important. HOWEVER, if there were one that also had a flashing led on the butt end, well that would be super-duper swell.
And yes, I am looking for the outside diameter of the widest part of the light.
I would like to have at least 1mm (ideally 2) around that for a gasket/vibration damping solution as well.