These are really nice, easy to use, and simple to understand. You can check male and female threads to confirm them and find out what size you need. I've already discovered a metric screw in a light and ordered a replacement because none of my local hardware stores carried what I needed. I was able to do that without carrying a sample to the hardware store and using their screw gauge.
Some review claimed the thread sizes on each piece were just stickers. Not true. They are etched into the metal. I suppose the paint might wear out, but it could easily be replaced in that case.