I have been unable to find threaded stem wheels for 4 iron patio chairs because the threaded holes on the legs are only 7/32" in diameter. What do I need (tools and bits) to enlarge these holes and leave the holes threaded so that I can acquire threaded stem wheels to screw into the holes?
You need a drill to enlarge the holes to fit you bolts, and a "tap" to thread the hole to fit the bolt. Tap and die sets can be bought from any DIY place, or try Screwfix.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix drills.