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:
Transmission Mount Plate
Product Details
Brand: Welder Series
MPN: 216351
Country/Region of Manufacture: Canada
Thickness: 3/16"
Hole size: 7/16" slots
With two slots for 7/16" bolts on 1-½" centers for a GM rubber mount. Overall size 6" x 2-½".
Used with #216352 or #10102 gusset for square tube crossmembers.