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:
Gusset, 3-7/8" x 3-7/8"
Product Details
Brand: Welder Series
MPN: 25402
Thickness: 3/16"
As supplied in our Chrysler motor mount kit.