Haven’t built a flashlight before, so it might be more legitimate than rhetorical. 
Our old house still has a fair amount of copper in the ground. Though the sprinkler bodies appear to be brass, the (L -shaped) risers are copper, threaded at both ends and screwing into PVC coupler.
This morning I started out to just twist the body off of a riser, but the copper riser twisted before the threads would let go. So I got to dig through about 8” - 10” of root to get down to the plastic.
This is what I pulled from the ground:
Well, actually the coupler came off of the spare I had in the sprinkler parts bin. I re-used the threaded coupler when I replaced the copper riser and sprinkler with spares.
This isn’t the first copper piece I’ve pulled out and thought about using for a light. But with this is it seems like it would be easy to put a cap on the end with a spring in it for the negative and use the plastic coupler as the head with lens or TIR optic. Unscrew the head for lockout, and to change cell. The PVC head would require the LED heat to go into a pill and turn on when twisted to contact pill to copper body. As is, this might be a fun little light for the workbench.
The 1/2” copper pipe will not hold a 14500, but a 10440 will work.
The coupler is just under 22mm ID for an optic or lens. Stack height will be about 35mm.
I’ve got some 20mm sinkpads, a spare XPG2 and a dedomed XRE sitting around, but a Nichia might be better.
Direct wire with resisters like OL did with that Solitare?
Post some ideas, maybe I’ll actually do something with this hunk most would toss.