7-Piece M35 Cobalt Left Hand Drill Bit Set for Removing Damaged Bolts and Screws, 5/64-Inch, 7/64-Inch, 5/32-Inch, 1/4-Inch, 19/64-Inch

Never Know with Amazon tools. Theses left hand bits cut through German steel like butter. Hoped it would catch and unscrew the broken screw I was working on . Once the pilot was done, a quick enlargement and a easyout finished the job. Bits are functionally sharp, as far as durability, hopefully I won't need them often. I'd buy them again.

These are fantastic drill bits! I had a broken 8.8 bolt inside the recessed end of the crankshaft on my RZR. I carefully drilled far enough into the bolt to spin it out with an extractor. If this hadn’t worked I’d have had to pull the engine.

These are made in China, but worked pretty good to drill out the broken set screws in a couple of the hose bib backflow valves that came with my house. I used a 5/64" and 1/8" drill bit to drill out the set screws completely, using a 3,000 rpm drill and progressing slowly so as to not drill through the hose bib. You can feel when the set screw has been drilled out and you've reached the softer brass of the hose bib threads. The reason I got these left hand drill bits was in the hope that the set screws would catch during the drilling and unscrew themselves, which they didn't, but at least they didn't tighten any more as they might have with a right hand drill bit.

Used them to try and remove broken manifold bolts. Turned out to be a one time use. They got dull quicker than I thought but did work for the two bolts.

Haven’t had to use these yet. It’s better to have them and not need them, then to need them and not have them. They look to be built well and can’t wait to use them. Learned that from an old head in the oil field many years ago great quote to live by if you are a mechanic.

I bought these for a broken bolt in an a frame, trying to swap a control arm. These cut nice and I was able to get hole in bolt. Unfortunately my bolt still stuck, but only because I need bigger bits now.

These bits were average at best...didn't cut even at low speed, moderate pressure. 2 out of 4 broke, now I'm switching brands. Had higher hopes but unfortunately they did not do the job as stated on description.

Greatest drill bits I have ever purchased. I had a starter bolt that snapped in the block. The piece was roughly an inch deep into my cast iron diesel engine block. Once these reverse drill bit latched it immediately pulled it out. It did not snap and dull like the previous ones I’ve used. It truly relieve a large headache I had. Highly recommended.

Got broken bolt out of engine casing now problem.