I previously had my FourSevens Atom on the keyring, have carried it as part of my EDC for some years now in various iterations but it is a 16340 light and made from stainless steel, titanium is my metal of choice so I had a go at making something similar in Ti to match my other titanium EDC carry tools.
Comparison. The 47s Atom had also been modified with a similar magnetic holder, through switch etc.
The bayonet locking system is really simple, just drill a hole into the shell, tap it, mark the other piece for the slot, partially screw through around 0.8mm a tight fitting machine screw along with jb weld and once set file it flush with the light body. 0.1mm titanium sheet stuck in backing the slot.
Of course waterproofing is an issue without machined threads but my pocket lights never get wet, I haven’t fallen in the moat yet 
the internal body does butt up against an o-ring and the internals are potted.
Best I can do with hand tools.
On lights that I convert to tail E-switch, if there is not enough width in the battery tube to insert a switch carrying signal tube like there is in the FW3x lights you can make a simple insulated thin metal bar that goes from the momentary tail switch that connects to a contact plate on the driver.
I make a copper contact disc just smaller than the internal diameter of the flashlight head, solder on a 30AWG switch wire, drill through a safe spot on the driver, pass the wire through, solder to the E-switch terminal and pot the contact disc onto the driver.
Like this:
Or:
Novatac 18350 conversion:
Thanks guys :+1: