screw

Maybe a stupid question but I can't answer it with Google so it is time to ask. There are lots of small screws and nuts used for mounting motors and other things. I can find size checkers for SAE that go down to #1 but I've come up short on the metric. Do these exist? How do you guys identify...

Hi, was recently changing the arms on my Quad for differently coloured ones, and when trying to tighten the screws, they seem to start slipping, first feeling resistance, then it becomes less as if the threading was failing, I stopped immediately and felt if the motor is fitting tightly and it...