I have noticed on this forum a lot of people talking about the use of thermal paste on the pill threads. Has anyone tested how this would affect the resistance? I’d love to know if this affects the tailcap current in the slightest.
I would not expect a measurable effect, but in principle it would be better to use a paste such as graphite or finely divided silver metal that conducted electricity as well as heat. Some such would probably conduct heat better too.
Thermal compound only fills the voids between two parts, where you had direct metal to metal contact before adding the paste you will still have contact afterwards if it's assembled tight enough. The voids filled by the paste weren't conducting any electricity anyway so filling dead air with paste isn't affecting the electrical part, only the thermal part.
If you DO find that the current is reduced afterwards, you either didn't bolt it together tight enough or the design of the parts means it can't be bolted together tight enough to squish the paste out of the way where it's not needed. So if making things tighter doesn't fix it, don't use paste.
On stuff like C8s I only use a little paste on the outer lip on the pill that seats against the head, but not on the threads. On lights where the pill or plate or shelf doesn't have to carry any of the electricity you can slather it all over everywhere with no worries... but it still has to be screwed together tight for the paste to make any improvement.
Exotic stuff is great where you have 150 watts of heat being moved through a tiny 1cm2 CPU die and into a massive heatsink, in flashlights, not so much. Go to Radio Shack and get a giant tub of cheap white silicone-based thermal goop and just build stuff.
I’m guessing with something like arctic silver it wouldn’t be very measurable. But some people use silicone based pastes
A good thermal paste should have good flow characteristics. Even the the non-conductive types won’t have particle size big enough and shouldn’t be so viscous that it prevents much (if any) metal to metal contact. If the pill is fully tightened, it’ll have a whole lot less resistance than any of the other contact point in the circuit.
Anywhere aluminum is in contact with copper, a galvanic reaction can occur over time if conditions are right. It might not happen within the confines of a sealed light but it doesn’t hurt to use a little thin oil or grease to displace the air between the threads.
IMO, using AS5 will lower resistance if anything by filling some of the microscopic voids with silver.
I think grease or wax is harmless here. It is the solid particles that could cause trouble.
I received a Black Cat light with something like Loctite on the threads between the body and head. It didn’t work reliably until I managed to get it apart and cleaned the stuff off. That stuff may have expanded on curing, or something else odd.
(Incidentally, where I know the silver conducting paint from is coating an experimental stealth shape, to simulate solid metal or carbon fiber, to measure the radar cross section.)
I've tried this but can't really tell how much it helps thermally. It's a bit messy, grey stuff, so I don't recommend
it where you'll be opening the joint frequently such as the tail cap threads.
http://www.homedepot.com/p/Ideal-NOALOX-4-oz-Anti-Oxidant-Compound-30-026/202276208#.UiyHFfm9Ucs
Looks good.
Works great for aluminum No OX ID is for stainless and metals other than aluminum. I put some on mine and makes the threads buttery smooth...started using this as well
Make sure your goo is oring friendly, don’t hope for miracles.
I don't think I've ever seen an o-ring on a pill. 
I've only ever seen an o-ring on a pill once. 
It looks like the nose cap is screwed onto the pill, that is screwed into the battery body...hmmmm
Subject is pill goo, but discussion went to goo on threads, and lots of threads have related orings.
Even with goo on the pill, lots of goo likes to migrate, so unless you want to periodically clean, best to use something oring friendly.
Most zoomies I have seen have the head slide over the front of the pill, with the back of the pill screwed into the body. They have either springs to control the slide or o-rings that also provide some water resistance. An exception is the TrustFire Z8 where the heat has to go through the stainless steel to get to the aluminum head, but only through its small thickness. Perhaps I should have silicone heat sink compound.