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 Base
Product Details
Brand: Welder Series
MPN: 15702
Thickness: 3/8"
Hole size: 4 holes 1/2", center 9/16"
4 holes are 1/2", center hole is 9/16". This clamp plate will not fit original u-bolts.
Grid is picture 1" x 1".