best bet, get yourself a good pair of vise grips (locking plyers). If you do not own a pair, you local auto parts store or Home center sells them. If you can not get them off with vise grips, you will have to take it to you local mechanic.
Have somebody WELD a rod onto the stripped plug & use that 2 turn it -- then throw the rod & plug away & put in your new drain plug with a new gasket for the plug.
If the screw is stripped then the threads are not holding and can be removed with pliers. If your asking, about the head being stripped, then you take a hack saw blade and cut a new slot in it,this way you can use a slotted screw driver to remove it. If it is locked in and does not come out, you will have to drill it out with a drill bit that is smaller then the thread size.
try a gator grip socket or pound on a smaller size
If the standard socket does not fit, ( 5/8 ) then try and find another size to fit, even metric. This is the best to do, other wise, you will have to remove the head.
To remove the cylinder head on an Astra 1.7 CDTI, disconnect the battery cable and remove the lower engine cover. Drain the cooling system and remove the oil filter. Remove the air filter hoses and disconnect the crank case breather hose from the valve cover.
You can purchase a screw extractor at a hardware store. This bit fits on the end of the drill and grabs hold of the stripped screw head and removes it quite easily. You could also drill through the damaged screw head about 1/8 to 1/4 inch. Once the screw head comes off, the screw shaft can be removed with a pair of pliers. firstname.lastname@example.org
To remove a pressed-in stud, you usually stack up a few washers and crank the stud out with an impact wrench on the nut. If the threads are completely stripped all the way down, you may have to take the head to a machine shop and have the stud drilled out and tapped for a screw-in stud.
Drain the radiator, remove the head, drain the oil, replace the oil filter. Install the new gasket and replace the head. Add the correct amount of oil and coolant to the engine. Start the engine and bleed all air from the system.
Hopefully you stopped once you realized it was stripped. If you did then your best option is to use a T7 driver and first tighten it (turn it clockwise) so that it can grab onto the un-stripped portion of the head. Then turn it (anti-clockwise) to loosen. Hope this helps. I tried this on my stripped screw on the Juliets and it worked. If it is stripped real bad and you went at it a few times then ideal would be to walk into an optical store and see if they can do it for you. cheers!
drill screw head out with 1/4 " drillbit mirror mounting plate can be removed by removing door panel. replace with new monting plate if threads are stripped in mounting plate. just did this myself