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:
Lower coil-over mount support block
Product Details
Brand: Welder Series
MPN: 21854
Country/Region of Manufacture: Canada
Hole size: 5/8"
3" x 1" x 1" with 3 holes, 5/8" dia on 1" centers.
Used with all our rear axle brackets to give the lower coil-over bolt more support. Welds to the ‘inside’ of the axle bracket.