A very important feature is the cartridge mount. It is screwed onto the motor shaft along the thread, and it is held from unwinding by a screw with a left-hand thread. The problem is that when unscrewing heavy fasteners, the cartridge unscrews a little along its thread (on the shaft) and the entire load falls on the small fastening screw. There are many cases that this screw simply breaks. Please note if you need to not only drill and screw, but sometimes also unscrew heavy fasteners.