How to fabricate and install Heavy Duty Threaded Inserts

Recently when channeling my Ford Model A I wanted to use Grade 8 fasteners for all of the body mounts instead of just tapping threads into the frame or inserting rivnuts that could fail over time. First of all the 1/4″ wall of the tubing wasn’t really thick enough to give sufficient threads to hold the weight and twist of the body from normal driving. We came up with a slick solution and figured we’d share.

I started by threading a batch of Grade 8 nuts onto a carriage bolt and locking them all together.


I then mounted the bolt into the lathe and cut off the hex portion of each nut leaving us with perfectly round grade 8 threaded inserts. The nuts were cut down just a hair bigger than 1/2″ so they would be a press fit into a 1/2″ drilled hole.






I then counter sunk each hole and threaded a bolt into each insert so I could adjust them so they were straight in the holes. I used the TIG 200 to carefully lay a weld puddle on the edge of the threaded insert melting it to the frame. You must take your time here and be very precise because a rogue dab of filler rod could go over the edge of the threaded insert and make your life hell when it comes time to thread a bolt back into the insert!








Hopefully you can use this method to put some clean, strong threaded inserts in your next project.



  1. That’s all fine and dandy if you have a lathe if you don’t have access to one what good is it

  2. what do you do with the raised bead, grind it smooth and you have nothing. I would run a 45 degree countersink in the hole before placing insert in it that way you have more weld grip and you can grind it flat

  3. If you reread the article and look at the pictures you will see I put a bevel in the frame to do just that. The weld bead was flush with almost no sanding needed.

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