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:
Radiator Mount
Product Details
Brand: Welder Series
Thickness: 3/16"
Hole size: 3/8"
Formed, 1-3/4" x 1-1/2" with a 1" gusset and a 3/8" hole. Designed as a radiator mount but can be used to mount other things. Available for Driver and Passenger sides.
I used this mount for the seatbelt anchor on the '32 build.