I fitted new M324 pedals to my Giant Roam 0. The old pedals came off easy enough with a pedal wrench. The new ones fitted first time also without any problems. But I realised I'd forgotten to grease the threads. They both removed again without issue but after I greased with Copaslip they both wouldn't tighten fully and ended up with the axle into the crank at an angle. I removed them and carefully cleaned out the threads of the cranks. I noticed there slithers of metals inside. It took two attempts at cleaning but both finally tightened fully without any problems. I'm wondering what I did wrong? I'd like to know for future reference. Surely it couldn't have been caused because of simply not using grease the first time? Many thanks.