When we ran a full service chassis fab/turn-key hot rod shop a number of years ago, it was always useful to have threaded things around to weld into the frame for some kind of mount, etc.
Here’s a list of all our threaded things for your reference:
Nylok Nuts
Product Details
Grade 5, zinc plated. Some available in thin sizes. 1/4-20 SS, 3/8-16, 5/16-18, 7/16-14, 7/16-20, 1/2-20, 9/16-18, 5/8-18.