|Don’t get 12 point sockets, those suck for rounding off bolts, unless of course you have 12 point bolts, not likely unless you have an aircraft or use a lot of super high rated AN bolts and stuff. Get 6 point sockets with a flank drive profile. This is the least likely to round off a nut and can even take off mildly rounded off nuts.|
Maybe the best way to prevent rounding off a bolt is to use the correct tools. I prefer to use 6 point sockets with a flank drive cam profile to remove stubborn bolts. I don’t understand why 12 point sockets are more common but a good six point with the cam profile goes a long way in not rounding off heads. Snap-On pioneered this sort of socket but now Craftsman and others make similar products.
Once you’ve rounded a nut or bolt, you’re screwed, right? Not really, but first you need to remove it. If a bolt extractor kit like the ones by Craftsman or Irwin doesn’t work, there are a few techniques I’ve had luck with in the past. You can soak a rounded nut/bolt in penetrating oil like Liquid Wrench or PB Blaster (my personal favorite is Aerokroil but its kind of hard to find) for about 5 minutes before attempting to loosen it with the closest sized open-ended wrench. Tapping the head of the bolt after applying Penetrating oil can help as well. Penetrating oil will reduce how much force is needed to remove the bolts. Heating a stuck bolt until red hot with a Mapp gas or propane torch, then reapplying penetrating oil often can help break loose a badly stuck bolt. Of course make sure that there are no other parts nearby that heat or flame might damage before trying this.
|Stick a big flat bladed screwdriver between the flat side of the nut and the wrench for more leverage.|
If the head of the bolt is impossibly rounded off you can use channel lock pliers or vice grips to grab the nut/bolt so tightly that it will twist off. There are special channel lock pliers that have rounded jaws perfect for this kind of problem. Or use a sharp chisel or cut off wheel to slot the top of the nut/bolt and then use a flat head screw driver to twist it out. If it’s rounded on one side, use the blade of a flat head screwdriver as a wedge between the wrench and the flat side of the bolt for more leverage. You can also try filing down the side of the rounded nut/bolt with a metal file until it is flat, providing two flat sides on opposite sides of the bolt head. And as a last resort, you can always cut off the head of the nut/bolt carefully, provided you have some way to remove the remaining piece of the nut/bolt. Obviously, never reinstall a rounded nut/bolt or one that seems it will become rounded if you look at it funny.