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:
Buick motor mount plate, 4 hole
Product Details
Brand: Welder Series Inc.
MPN: 380251
Country/Region of Manufacture: Canada
Thickness: 1/4"
Unit of Measure: EA
Used in our #380200 engine mount kit.