A: The answer is easy… Don’t ever use either one in your vehicle locks. WD-40 and similar petroleum based lubricants can, over time dry into a sticky film that not only inhibits the moving parts inside the lock but also traps the dirt and road grime leading to all sorts of lock failure. Graphite is the lubricant of choice for house, office, hotel type locks. In this application it works great. Vehicle locks are a whole different animal. Because the locks come from the factory pre-greased, putting graphite in them is only going to make mud. For the health and longevity of your vehicle locks we recommend using a Teflon or silicon based lube. These are found in most hardware and home improvement stores. The particular brand that we use is Tri-Flow, but there are many others that work just as well.