How do you choose the right lock washer for the job?

I don't know which lock washer is the one to use...I am attaching brackets to a plastic console and I don't know which is best. Do the lock washers have to contact metal (like another flat washer)?How do you choose the right lock washer for the job?
It is better that both sides of the lock washer are in touch with a metal surface, but if it is impossible you can use a flat washer on the non-metal surface.How do you choose the right lock washer for the job?
A flat washer under a lock washer defeats the purpose. what a lock washer does is dig into the surface and the bolt to keep the bolt from spinning, if there's a flat washer in there then the flat washer turns with the bolt causing the Lock washer to be ineffective.





Lock washers will mar the plastic, But only under the washer where you cant see it.





If you're nervous use some Locktite and a flat washer.
Plastic isn't that resilient,so,I'd use a large flat washer and a nylock self locking nut.
black is right use a lock nut