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 Frame Mounting Kit
Product Details
Brand: Welder Series
MPN: 108140
Thickness: Main plate 3/8", gusset 3/16"
Hole size: 1-1/2"
Use this kit as the frame mounts for stock-style Mustang II strut rods.
The strut rod washer is used to tighten bushings that are loose on the 3/8″ bracket. The gussets are 3/16″, main plates are 3/8". The center of the 1-1/2″ diameter hole is 2-3/4″ from the opposite side. That edge is 2-13/16″ long.