I need to add to this thread, having just got 3 new lights. The one that *doesn't* fit is an 18650 Zebralight H604d.
Two that I think should be included are the micro-sized Olight i1R 2 EOS, and the Olight S1 Mini Baton HCRI.
The i1R uses a non-removable, ***non-protected*** 10180. Yeah, I know, CPF don't like this application. But for informed users, it's very capable, with 5 lumens / 7 hours, and 130 lumens for ~15 minutes (safely). It's the size of your two pinky-finger joints, and has a nice beam color and spread. It's definitely small enough for genuine key ring use. While I will always love my ZL SC52, I'm keeping the i1R in my pocket, a first for me. The new design uses a captured rear cap, so you can't lose it. It locks out when unscrewed, so it won't ever screw itself on in your pocket.
The larger (thumb-sized) S1 Mini has an 'ok' high-CRI LED, with a beam width useful for close-up work. Better yet, it has a good moonlight mode (0.5 lumens) and 16/64/326/684 lumen steps. 326 L for 1 hour. These steps are similar to what I programmed for my SC52. Press and hold the side mount button for ML, press and hold for the next three steps, or double-click (from off, or from on) for turbo. It retains any of the last-used middle three modes for next time use. I like this better than the ZL interface. There's a 'charge me now' LED in the side button.
Anyway, that's my contribution to offset the help and knowledge I've gotten over the last 10 years.