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:
Alternator Mount Tensioner
Product Details
Brand: Welder Series
Country/Region of Manufacture: Canada
Thickness: 3/16"
8" long overall with a 5/16" hole and a 3/8" x 2" long slot.