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:
Aluminum Spacer
Product Details
Brand: Welder Series
MPN: 30213
Country/Region of Manufacture: Canada
Diameter: 1-3/8"
Length: 1-3/8"
Hole size: 5/8"
This is the aluminum spacer used in our coil over bolt kit.
1-3/8″ diameter at the large end of the taper.