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 Saddle Plate
Product Details
Brand: Welder Series
MPN: 21154
Thickness: 1/4"
Hole size: 7/16" slots
2 slots for 7/16" bolts on 1-1/2" centers for a GM rubber mount.
3-1/2″ front to back. 4-3/4″ point to point. Designed to be used with #211522 transmission mount side plate. 1/4″ steel.