Washers. One of the things I noticed during the Metric Mechanic trip was that they preferred to use “wave” washers. Wave washers aren’t flat so they have a little “locking” functionality.
I have a lot of spare fasteners. Some from buying sets of fasteners and others from parting out cars. They’re all pretty organized, but somehow I often don’t have washers in exactly the size I want. BMW seems to like washers with small outside dia.'s, and the washers I end up with from the autoparts store sets are a fair amount bigger.
Today I finally got around to buying the wave washers that MM used. Go to Amazon and do a search for pico “wave washer”.
Another thing that MM did is to send used-but-serviceable fasteners out to be replated. Apparently it cost them ~ $100 to get a quantity of fasterners plated along the lines of half a Home Depot bucket. This really made them turn out terrific. For no good reason I’ve really come to like shiny new fasteners. I’ve been kicking around the idea of getting all my old fasteners plated.