NET0320-K  NET0320 -K LEFT HAND 13 Piece Drill Bit KIT Must Have For Broken Bolt REMOVAL!  1/16" to 1/4" inch bits
Very handy for removing broken bolts, studs etc. We have great luck using Left direction bits for removing broken bolts. Some do not have the same experiences but we have a 70 percent success rate with bits alone.
 
SHOP TIP- Make sure the drill is in "reverse." Try to have the the face of broken bolt as flat as you can if you can with a grinder, die grinder or punch. Center punch the bolt so the bit has somewhere near center to start. Use the smallest bit within reason for the bolts size but not too small as the bit has to be big and strong enough to spin/break free the bolt. And if the first bit does not do it you can keep tying with larger bits to have more chances. 
          The key is learning the right amount of pressure and a SHARP bit. You don't want too little pressure as the bit wont grab hard enough when it catches to spin the bolt and too much pressure and you just are drilling a hole and cutting. What you actually want is what you don't normally want when you drill normal, you know when a drill "CATCHES" and damn near twists you arm, well in this case that is what you DO want but the idea and hope is since drilling in reverse with these bits it "CATCHES" and all that force twists the bolts loose and not you arm. 
          Some other tips, Drilling a small hole all the way through can help relative pressure and make the bolt easier to free up, penetrating oil ahead of time on the treads helps but brake clean spray the bolt clean before drilling as in this case you want sharp contact and friction with the bit and bolt not oil. Your not worried about saving the bit but removing the bolt. Heat is always your friend if you can safely heat the bolt hot ahead of time do so and hit it with a center punch when hot. Let bolt cool before trying to drill. GOOD LUCK and may the force be with you! When they work you would have paid 5 times the price for saving your butt
 
OPTION- To add Punch Kits and Tools
 
NOTE- We offer quality tools at fair prices, often many of these tools we use here or at the least tested them first hand and have been very happy with the quality and performance! That said they are offered with affordability and ease of use in mind for the "do it yourself-er" " they are not professional tools meant for 10 hours a day 7 days a week but are also a tenth of the cost of most of those caliber tools.  Finish/appearance, markings etc may very. ALWAYS PRACTICE SAFE PROCEDURES AND USE PROTECTIVE GEAR