This is a slippery slope. Most lights don't state their diameter, at least so you can understand it. And most mounts are for 1" lights.

I have found the best solution (for me), is to use the streamlight pro tac 2 or HLX rail mount light with an Arisaka scout mount. This gives you a very secure mount, and it is very close to the rail. You can get the mount in either keymod or mlok and the light will mount to either of these. The light is available from 800 to 1000 lumens and works great for my use.

Good luck with your search.

Rick