maintenanceguy wrote:Oil is bad for locks because it gums up the small parts (pins) when dirt gets into the lock. Graphite isn't sticky so this doesn't happen with graphite.
Bur for a practice lock, who cares if it gets gummed up in 5 years. You can just flush it out and it's good as new.
WD40 or any light oil such as 3 in 1 will work fine. And a little goes a long way. No need to over think a couple of drops of oil.
Just my 2c, but I have found 3 in 1 too viscous. WD40 or even kerosene will dissolve gummed-up lube pretty well. Graphite started being used when locks had large sliding parts with lots of clearance-it usually ends up in the bottom of mortise lock cases. It would be OK if only used ONCE, but I have seen locks so full of it the pins wouldn't move.