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:
Front Sway Bar Mount, 1-1/4” tube
Product Details
Brand: Welder Series
MPN: 213082
Country/Region of Manufacture: Canada
Thickness: 3/16"
Hole size: 5/8"
Formed and notched to weld to 1-1/4” tubular lower arms when you want to use a Chassis Engineering (the street rod parts company) Mustang II style sway bar.
The hole is 5/8″ diameter.