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:
Front Four Link Frame Bracket Plate
Product Details
Brand: Welder Series
Thickness: 3/16"
Hole size: 1/2"
7-1/4" x 4-3/4" (approx) x 3/16" thick with 2 holes 5/8" diameter on 5-1/2" centers.
Used in the Model A rear 4-link frame bracket when the rear frame rail tapers. Sold individually.