Best conductive material to bridge gap?

I have a Nitecore MT10C which I want to use with the large Thyrm Switchback, but the interior flange which holds the latter in place spaces the tailcap so it loses its connection with the bottom edge of the main body.

I can make a conductive spacer without much difficulty but I wonder what material will do the job reliably without needing a lot of maintenance (i.e. cleaning oxidation to maintain the connection). Aluminum? Copper (I presume not)? Brass?

Is there some sort of ready-made springy accessory I can get and just drop in for this purpose? (The light takes 18350s.)

Thanks!

I ended up trying some 18 ga. aluminum wire I had, which I bent into a continuous 'S' shape. With a little force it made the light work with the Switchback in place. I would not consider this solution reliable, as I had one instance in which the tail cap loosened just enough for the light to stop working, although it felt tight.

Well,
Electric wire uses copper.
Flashlights use brass or alluminum. But I'll say this...when I had my house re-wired from alluminum wire to copper my light bill noticeably dropped.

I have no idea what diameter, etc. you are looking for:

http://www.oveready.com/hardware/beryllium-copper-spring-washer/prod_295.html

I have no idea what diameter, etc. you are needing. Here's a beryllium copper spring washer.

http://www.oveready.com/hardware/beryllium-copper-spring-washer/prod_295.html

Use an 18500? You'll get a little more capacity but I understand not wanting to buy new batteries. Not to mention I don't know how much space you need to make up. Mtnelectronics has springs as well as some neat little brass buttons.

Thanks everyone. I had wondered about beryllium, those spring washers look just the thing, if I can find one that compresses to a little less than 1 mm, and is around 20 mm in diameter.