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:
Clamp Plate Crossmember Tab
Product Details
Brand: Welder Series
MPN: 15710
Thickness: 3/16"
Hole size: 3/8"
Used in our #15710 U-Bolt Eliminator kit, welded to the crossmember. 3-1/2" x 1" with a 3/8" hole.