Imperial, SAE, or whatever we call our inch based hardware here, the bolt thread pitch is measured in threads per inch (TPI). Metric bolt thread pitch is the distance in millimeters between threads. For imperial hardware a higher thread pitch count means the bolt has a finer thread. For metric bolts, a higher thread pitch number means the bolt has a courser thread.I do not have a few metric taps but not an M6x1 (I thought the "x1" would refer to threads per inch / tpi)