A few years ago I started using petroleum jelly as a lube for my knives on the locks. Works great and non toxic. Last years started using it on the flashlight threads. The non anodized threads always oxide and blacken up the oils used. Petroleum jelly seems to stay cleaner and being a grease might improve water tightness. Am I missing anything or is this a good use of the stuff?
I think that petroleum jelly can cause rubber to break down. My understanding is that to avoid this one should use silicon based products instead of oil-based.
By the way, a bit off topic, but if you use petroleum jelly to moisten your lips (or other parts of your body), I recommend Aquaphor instead.
It’s more expensive than petroleum jelly, but you can save some money by purchasing 14 ounce plastic jars. 
It’s what I use, and it’s a lot nicer than regular petroleum jelly. 
There are better greases for that, as petroleum jelly can damage the o-rings if they’re the wrong material.
Generally I recommend grease for the threads of a flashlight instead of oils, as they don’t run out when the light gets hot.
Try some Nyogel 760G, it is my go-to flashlight thread lube. You can buy it on amazon, the 50g tube lasts forever.
Ford Motorcraft XG-12 is the same grease in a different label, in case you can find it for cheaper.
https://www.amazon.com/Genuine-Ford-XG-12-Electrical-Grease/dp/B000NUBB28
2 Thanks
Not if they’re silicone o-rings. This argument has been going on for years, I’ve never seen an o-ring broken down or dissolved by any lubricant, but I have seen them break from a lack of it.
2 Thanks
Found this thread:
1 Thank
I tend to agree, using olive oil is bettter than using nothing.
Quite a few of my lights use a mix of black, clear, and red o-rings (most notably, Hanklights), which is why I recommend a grease that is compatible with all of them.
I’ve seen nitrile o-rings being red sometimes.
Can never be sure what kind of rubber is being used, especially because we don’t know what OP has.
Also, a note about Nyogel and other greases: make sure to fully clean out the old grease in the threads and below the o-ring. The thickeners can interact sometimes, causing the grease to separate or clump up. This can happen with other lubricants too, not only Nyogel.
2 Thanks
Yes, petroleum jelly is used as an o-ring and thread lubricant. Maglite uses it on their flashlights.
Petroleum jelly and mineral oil are highly compatible with Buna-N / Nitrile o-rings (which are the most common o-rings) and these lubricants are inexpensive and available in any grocery store. They are also non-toxic.
4 Thanks
Ya go ahead. Totally fine. I’m not a fan, too gooey, but if it works for you go for it.
Nyogel isn’t compatible with everything eh? PAO?
Nothing is compatible with everything, but it is compatible with almost everything (unless you’re purposefully looking for incompatibility), I’d call it good enough.
Also found a datasheet.
https://www.candlepowerforums.com/attachments/tds_english_nyogel-760g-pdf.28403/
1 Thank
Well fluorinated grease. But PAO is incompatible with lots of stuff. All the same stuff petrolatum is.