I often get asked questions about Noalox and why it's so beneficial to use it on our mechanical mods.
Virtually every well-known mechanical mod manufacturer recommends it and many even ship their mods with Noalox pre-applied to various parts of the unit.
In a mechanical mod, the current is having to "jump" from one part of the mod to another.
Oftentimes, no matter how carefully you clean your equipment, some invisible oxidation or particles can remain on the contact points that interfere with the full current flow, or indeed, on the battery contact points themselves.
Noalox is a substance that contains zinc particles which conduct electricity. Using it on the contact points of your mod, bridges any miniscule gaps that may be caused by oxidation or dirt, or just a battery that's not as flat as it could be on its contact areas.
Additionally, the current must flow up the main tube, so any threaded joins that you have in the unit, can benefit from Noalox, both to keep the threads working nicely, and to ensure contact is maintained all throughout the threads.
I have seen some people talking about using petroleum-based products, however, this is a bad idea, and here's why:
Petroleum based products are non-conductive, so whilst they may make your threads operate all nice and smoothly, they may actually impede current flow. However, if you have threaded parts on your mod that frequently come into contact with juice, (such as within a juice feeding tank), petroleum jelly is the better product to use here to keep threads flowing freely, but only in an area where current is not expected to flow.
Hope that helps explain the situation.