You either need to know the size hole they fit or goes with each tap in order to choose the correct one to make a threaded hole or you need a tap and die chart listing all the different size holes they correspond with. The die is used to re-thread a bolt/thread that has been damaged or to thread a rod for use in a threaded hole or nut/the female part. The tap can be used to repair a threaded hole/nut or to thread a hole to make it work with the right threaded bolt/screw/fastener. You will need a bottle/can of oil/tapping fluid so the tap does not heat up and become galled/stuck in the hole while making the threads. You place the tap in the handle usually a adjustable nut to clamp/tighten down on the tap and hold it in the handle . You place the tap point down in the hole that is to be tapped and press down while turning the tap. After you start the tap and make a few turns cutting the threads into the sidewalls you back it out in reverse and put some tap /cutting fluid on the tap then repeat until you get close to either the bottom of the hole or are ready to break through the other side. Back the tap out(counter clockwise unless it is a left hand tap) blow out the hole and add more cutting fluid then finish the hole . You should now back out the tap and have a finished tapped /threaded hole.I hope I explained this well enough. Later