I had a problem with the thread on a ITP A2 that was solved with cooking oil.
Thicker than the magic greases that I tried earlier.
Cooking oil will congeal over time and make a sticky mess. There are thicker silicone greases available. Try a plumbing supply house. I picked up a dozen mini tubs of some awesome waterproof silicone grease there. One tub is a lifetime supply… or better yet, some Marine grease from a marine supply.
I put silicone on the o-rings, but with that I have from a hardware store the aluminum on aluminum threads gall. I am using mostly furniture wax composed of carnauba, bee’s wax and orange oil. I probably should find some sort of automotive grease. The furniture wax hardens somewhat as the orange oil evaporates out of it, but it still lubricates.
Silicone with good thin film properties might be ideal, but I am not sure it exists. Silicone is not the strongest material for o-rings, so it is probably better to use ordinary o-rings and a silicone grease, if one can find silicone that works well for lapping together machined aluminum threads. I read of lights with anodized tail cap thread, but I don’t have one. Some of the bezels are anodized, and those present less problem.
To better protect threads, at a pool supply I found a few tubs of an excellent and thick silicone grease that is VERY thick and sticky. It feels almost like an adhesive.
A pool environment is harsh…It has to be waterproof and handle heat and chlorine under pressure so it’s tough stuff.
A moly amplified, high pressure grease will prevent metal galling, but it’s black. Silicone grease can be modified with moly…I’ve modified silicone grease with HBN; it’s much slicker than moly and white…but all this is overkill for this application.
I’m currently using a dry bike chain lube spray for threads and o rings…good lube and it’s dry. Any carnauba wax would work, but the spray is better engineered and a lot more convenient.
If you don't want to use a grease, wrapping a layer of copper tape around the threads helps tighten things up and makes the threads glide better. Also helps with electrical connection. The threads bite through the adhesive. I just don't use it on pill threads anymore. The heat gums up the adhesive and encourages a galvanic reaction with the aluminum.
Thanks Cat and Wheelr. Those all sound like good suggestions. I have bike shops near. Yes, the chain needs to be lubricated but with as little mess as possible, so silicone chain lubricant should do well. Nice to know it is just the particular stuff I have that is bad in thin films.
I may have some thin copper with my model airplane stuff, but where did you get the copper tape and what was it called? I gave up on one $3.50 SK68 clone because the threads were too loose. If a better light has that problem, I suppose copper tape will help it. I believe that hard aluminum alloy has copper in it and that is mostly why it corrodes faster than pure aluminum does, but I can see that adding copper could increase the electrochemical problems.
I just got mine from some ebay vendor. It was so long ago, that it's not in my history. So I don't know who I got it from. A little goes along way which is good because it's not cheap. Copper tape can be used to cure a lot of different issues in lights. Maybe my most used supply.
I know there are different types, but I don't have any advice on that. Anyone here have some copper tape advice?
Copper is great for heat sinking, but if you use it for electric conduction by contact, you need to be careful if it's treated or not, if not, then corrosion will occur and it may be totally invisible. Not sure what the best option is, but cleaning/treating maybe necessary for longer term use. Old-Lumens had found this out when several of his modded lights were out there and having intermittent issues and failures - he posted a very informative thread/video on it a while back.
Copper pills for example, count on the threaded contact with the aluminum body for conduction, so I treat the threads with DeoxIT Gold, or equivalent.
Bike chains usually get a dry lube, pool valve grease can be some good stuff. I bought a tube at a yard sale one because it was actually rebranded I think its called dupont Krytox, about as good as silicone grease gets as used in vacuum valves etc. and oring friendly.
Good idea, I use Silicone Grease from a Mill Supply store @ $10.00 / 4oz ~
You can get Dielectric Grease [Silicone Grease] from Autozone or Advance etc for about $3.50 for a small tube.
Permatex/.33 oz. (9.355 g.) dielectric Tune-Up grease
Wow, first time I’ve heard someone use my term, “Invisible Corrosion”
It’s very widespread throughout the DC world, sometimes you get lucky and see a transparent golden coating but usually not.
Well, oxidation that's hard to see? 
We [mechanics/electricians] at my workplace use this term for any condition of non-current flow that is caused by this issue.
One time I had a oddity, my coil would not fire through the end, inside was Rust.
Iron is conductive, right ?
Not this time, I had to eat it out with hydrochloric acid before it would fire again…
Not invisible, but similar. Looks iron-oxide would connect, but not…
At the bike shop, I didn’t see any silicone but got some chain oil with “boron nitride nanosized platelets”. That appears to be a substitute for graphite that isn’t black. So far it seems good, but I still put the silicone on the o-rings.
Any links to the DC world, I like making good connections. Part of my toolbag is big tube of Oxgard, silicone greases with zinc particles to pierce the surface corrosion on contacts.
The chain lube I use is a “dry” lube spray that dries after application and leaves a dry film that is slippery but doesn’t attract dirt like an oil based lube does…that is important on a bike chain.
Zinc is not much of an abrasive, but it is a more active metal than copper or most others that might be used. Perhaps it reduces the oxide back to metal in spots, restoring the connection there.
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Any links to the DC world, I like making good connections. Part of my toolbag is big tube of Oxgard, silicone grease with zinc particles to pierce the surface corrosion on contacts.
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There are more than one type of silicone grease.
For purposes of this forum, typically AFAIK, we’re speaking of the clear “dielectric” grease.
The white thermal heatsink type used on CPU’s will work on die-pill-fin sinking, common name Arctic Silver.
Common theory is clear dielectric silicone grease is electrically non-conductive .
If it coats contacts, it “may” prevent continuity.
However, if the contact is tight mechanically, the grease will be forced out of the connection and continuity will be maintained.
I cannot validite this claim,
$13+ w/s&h.
“Use on any electrical connector to improve conductivity”
Camco Electircal Protectant and Lube
For a Conductive Adhesive
$4.00 @ newegg
Silver, Electrically Conductive Paste Adhesive for Electronics Repair Applications PCB Repair
http://www.newegg.com/Product/Product.aspx?Item=9SIA2C51705201&nm_mc=KNC-GoogleMKP&cm_mmc=KNC-GoogleMKP-*~~pla~~*~~Thermal+Paste+%2F+Grease~~\_–9SIA2C51705201&ef_id=UlR5wwAAAVx96bkI:20131207214047:s
Any industrial members grab some Thomas & Betts Kopr-Shield, great product.
A 4oz bottle will last 100 folks a lifetime of regular usage.
Yes, aluminum threads are a bit complicated, on the thin film level. The bare aluminum alloy will oxidize if not coated. A thin oxide coating prevents further oxidation but at some thickness it will prevent conductive contact. Any water repellent lubricant will prevent or at least retard oxidation. The bare aluminum alloy will also gall when the threads rub, unless it is protected by a thin film lubricant, but I am not sure whether too thick a lubricating film might interfere with conductivity. Electrical wiring in houses was made of (purer) aluminum at one time, but there are problems with the connections. I don’t know if the conduction electrons can move across a very thin dielectric coating, perhaps by tunneling, or whether there are spots where the coating is forced out.
Then there are the o-rings. As far as I know, only silicone will not soak into the rubber, unless one uses silicone o-rings that are not as strong as ordinary ones, but I suspect that waxy lubricants may also be alright.
FYI the issue was with the connection between aluminum wire and steel screws in switches and outlets.
Per the NEC [National Electric Code] the wires must be “pigtailed” using copper wire and the copper+al connection made using a Nolox type compound and placed in a box with accessible cover.
For those with aluminum wiring, or Cu for that matter, a simple check is to feel the cover on the switch/outlet.
If it’s hot, cut the circuit and have it repaired.
Loose screws on outlets feeding freezers or fridgs burn down many houses yearly… TIGHTEN them all for safety.