Originally Posted by
spinerguy
Agreed.
Thread failure is evidence of user negligence. It is your responsibility to make sure extractor nut is properly resting on cranks’ base before proceeding to extract. I know sometimes you have metal shavings (or rock granules for that matter) that can get it stuck tricking you into believing is fully engaged.
When you fail to do so, sharing force are then exerted or transferred to the threads which are not in any way designed to support this load.
This response is evidence of reading negligence. He clearly stated earlier that the crank arm was stripped smooth all the way down to the base of the extractor threads. Taking what the OP has said at face value, he used the extractor correctly and the threads gave out. This clearly isn't a common occurrence, and the vast majority of stripped threads result from user negligence, but why is it so inconceivable that the threads on a single 75 arm were faulty? Even the tightest manufacturing practices have some non-zero failure rate.