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:
Plate for Bolt On Shock Mount
Product Details
Brand: Welder Series
MPN: 10305
Thickness: 3/16"
Hole size: 5/16"
3-½" x 2-3/8" with 4 holes 5/16" diameter. Designed to turn #1030 into a bolt-on mount.