Standard machine fat would do the job. Just keep in mind to get fat instead of oil. Oil is made for enclosed applications, fat is for bearings etc. that are exposed to the outside. You should find such lubricant in your local hardware store. -Marius
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You can use bicycle oil. That works fine. Don’t use lithium grease because it’s really messy.
When in doubt the RepRap Wiki is a great reference. No matter what 3D printer you’re using, its roots can be traced to RepRap. Here’s the wiki entry on lubrication: Lubrication - RepRap 7.3k Good luck.
The bearings should be self lubricating. If you feel they need to be lubricated, then a little light oil or lithium grease, but just a touch - too much will cause other issues.
Teflon spray is the best
I use household lubricating oil.Personally I do not think there is a need for expensive lunricants since there is not enough friction to get the smooth rods or the bearings hot.
Nice one, Marius. 
For sure, your English is far better than my ( German? ) but I had to laugh. I think you mean grease ( schmieren ). Fat is either what you cook with or what you burn at the gym. 
Cheers!
AndyL
Yeah, I mean grease. But maybe fat works aswell 
I was bored in school and thought I’d check 3dHubs. Ja, bin deutscher 
-Marius
10 days later
1 year later
I use tamiya ceramic grease and works fine i also put some on the belts its for plastic and metal.