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:
Mustang II Upper Tower Boxing Plate
Product Details
Brand: Welder Series
MPN: 14308
Diameter: 10 ga
Upper tower boxing plate for Mustang II. 6-3/4" x 2-3/4", 10 ga. Priced individually.