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:
Strut Rod Bracket, plate only
Product Details
Brand: Welder Series
MPN: 30181
Thickness: 3/8"
Hole size: 1-1/2"
Has also been used as a Flathead motor plate. Laser cut from 3/8" steel.
The center of the 1-1/2″ diameter hole is 2-3/4″ from the opposite side. That edge is 2-13/16″ long. Priced individually.