keeping electrical conductivity on screw thread

Sounds like a gentle squish of the end cap will do the job...

Thanks. could you explain to a novish 'squish' ? would i need to do a degree course?

run a rough file over the threads

wrap a bit of foil around the threads.

He's got a screw loose. Didn't you read the post?

If this is a typical Maglite then trash it. The switch mechanism will never be trouble free after the light is a few years old.

Wrap a few turns of Teflon pipe thread tape around the male threads so that the looseness is removed. You might have to rewrap frequently, depending on how much use the flashlight gets. Another suggestion is to cut a gasket out of a sheet of very thin rubber or vinyl sheet, lube it with silicone grease and wrap the gasket around the threads.

won't that insulate it? ...

Actually, no. The contact between the lens housing and the body of the unit is actually made by the end of the body and a mating surface on the lens housing. If the Teflon tape is confined to the threads, the contact should be good. Also, the Teflon tape is extremely thin and is easily torn by the threads; providing more contact surface. The idea I was trying to suggest is to fill the gaps in the threads, reducing the tendency for it to unscrew itself.

If it IS a real MagLite, OP is mistaken about it being part of the circuit. You can actually take the nose off and use it as a base, and use the flashlight as a candle. (leastways, on the pre-LED versions) I suppose there are some knockoffs that use it as part of the circuit, but I have never seen any. Flickery light is almost always due to an internal spring getting wimpy.

(Note- even on a full-size Mag, the side switch is repairable. A pain to get it out, but repairable.)

-- aem sends...

FWIW, the OP didn't say it was a MagLite. (It helps to keep track of this stuff when I come in late and read the whole thread at once.)

Bend one of the threads a little bit. Not one at the open end. One 3 threads back, so that you can still use the good threads to start screwing it on, and they will be enough to pull it on when it gets to the bad thread.

If you don't do it enough, you can do it more later. (make sure it is meant to screw on that far.)

If you do it too much, you should be able to clean up the bad thread a bit by twisting a screwdriver in the groove.

Hi, I'd try a piece of Al. ducp tape.

Most of these torches have an o'ring on the bit you turn them on with.Get a new o'ring or one a trifle bigger.

Probably hi-jacked some other thread in one of the cross-posted ng's.

That sounds good too.

Or insert a piece of dowel, then crush the threads a little with a hammer.

Depends how sturdy it is. If it's an AA-battery sized torch then probably just a quick 'bite' or a gentle tap with a block of wood would do the job. If it's more solid then a (padded) hammer could do it.

The intention is just to make it very slightly out of round, so it makes a good solid connection and can't rattle loose.