I am having a discussion with coworkers about sufficient grounding to a chassis... my opinion is that a toothed ring terminal in contact with bare metal is required, e.g. Molex 19074-0025, so that the teeth will scrape through any oxidation layer:
(Alternatively a regular ring terminal with a toothed lock washer.)
Someone else suggested a Faston tab like the ones in the picture below:
I am uncomfortable advising use of these terminals, or any other connectorization of earth grounding.