Knipex's double-edged bolt and screw extractors, No. 9R 471 901 3, can remove damaged screws, studs and bolts and is servicable for years of use. The extractors remove damaged screws and bolts without damaging the threads on both right and left handed thread applications. Non-slip and double-edged engagement allows them to be used on even the toughest frozen bolts. The tool has four double-edged cutting/gripping edges. Simply drill the right sized hole into the frozen bolt, hammer in the extractor, and turn it out with a wrench or ratchet.
Eric Moore, a medium duty technician for DeMary Truck in Columbus, Ohio was given the double-edged screw extractor set to put to the test.
No one likes having to use extractors of any brand, because if you are having to take them out of the toolbox it is only because a pair of vice grips can't get a grip on the fastener and spin it out. Every technician knows what that means—time to break out the drill.
"It is a different design on an old process, but a well thoughtout application," Moore notes. "This tool is one that even in the best circumstance, you are using it because there is a broken fastener, which always costs time during a repair. All things considered, though, this extractor set was fairly easy to understand and use."
The tools came with some simple instructions in both English and German (due to their manufacturing origin). He observed that a drill size chart was included in order to point the technician to which extractor to use with what size hole.
"Preparation for use includes sizing the damaged fastener and comparing it to the correct size extractor," Moore says. "No complicated instructions for use."
Moore found that quite a few of the extractors' features really impressed him. "These tools have the ability to be used for either right-hand or left-hand fasteners," he says. "I also really liked the hex head design which gives you the option to use either a wrench or socket without having to use either a tap wrench or tap socket, because this helps with clearance issues."
Moore also listed that the tool's ability to be hammered into several different sized holes made it usable in more situations. However, he also found that the extractors shared limitations that differently designed extractors also had.
"As with all of the extractors, of many different designs, which I have used over the course of many years, the smallest sizes are very fragile," he explains. "The number-one size tool did not grip as well as I had hoped, and when driven into the fastener farther, it started to twist and felt like it would break if used further.
"I ended up just drilling out the broken screw and re-tapping the hole, which is pretty much the end result with any of the previous versions of extractors where I had to use the smallest size tool."
The verdict? "I would rate this tool an 8.5 (out of 10)," Moore says. "I have used several different designs of extractors. None of the other designs allowed for the right- and left-hand operation with the same tool."