Hey I have a simple, perhaps even stupid, question.
I’ve started taking apart flashlights and can’t figure out whether the O-rings are supposed to go between the bezel and lens, or between the lens and reflector.
On lights with a lens and TIR (like my D4v2), does it go between the lens and TIR? Or do those parts sit together and the O-ring goes again the bezel?
It seems if the O-ring is sealing out dirt/water that it will probably do its job in either position, so maybe I’m being dense…
Between lens/glass and bezel, usually. Both, preferably.
There is no direct answer. Different manufactures makes it different (and some of them make mistakes).
If there is round groove inside bezel, you have to put o-ring in this groove (in 100% cases).
If there is lip on top of the reflector, and o-ring can sit between reflector and head nicely (not falling down under pressure), you need to put o-ring (in 50% cases).
Tirs make things more complicated. Multi-led tirs rarely have extra room for o-ring, in most cases you want glass bigger than tir, and water seal between bezel and glass.
Multi-led tirs are not so rigid, you need to use proper size o-ring, otherwise extra pressure from bezel can damage tir legs.
If you need extra sealing (underwater usage etc), it is always a good idea to make a section drawing and check how it works in your host.
Thank you both for the info!
here is an example of O rings being used above or below a TiR, depending on which one is being used
I agree with the other contributions, that the O ring is often between the lens and the bezel
but not always 
I try to make note of where the O ring is, when I open a light… Ive had the same question you have… where does it belong?
Thanks for the picture!
I will definitely pay more attention in the future.
I think there is a lot of flashlight assembly/disassembly in the near future for me. Just stating out, but I’ve definitely caught the modding/building bug.
very happy to help support your modding interests
Im new to it also, and thanks to the great support in this forum
I have been enjoying the ability to swap my own LEDs
very satisfying experience for me… when things go right… lol
and very educational, when they do not go right
Agreed! This is a very welcoming place, especially for those like me with zero experience.
I’m having a great time taking stuff apart, swapping LEDs, and planning more ambitious mods and builds.
I’ve drawn a lot of inspiring scouring BLF…
Aaaaand?
Wellp, if you discovered The Secret, it’d be nice to share it, in case anyone else has the same problem.
Yea, that sounds fine. Thanks for sharing the info!
dontnknow if it was answered, too early for me to read whole thread, but in my d4/KR4/all Hank lights he makes his bezels with a groove for the oring to sit in. They go in the bezel "channel" on top of the glass lense. Hope,you get it back together 