Tapping a 7/16" X 20 TPI thread into 1/2" mild steel

Tool and die maker here and I’ll tell you that if you have just a few holes to tap, get a hand tap at the hardware store. First tap in trebig’s post. 3 or 4 flute. Spiral taps tend to break hand tapping if you’re not careful. I wouldn’t buy a tapping head unless you have lots of holes, just not cost effective. Thread forming taps displace the metal and no way can you drive it in by hand. Use paraffin as a lubricant/cutting fluid, I just use a candle by rubbing it across the flutes of the tap before each hole. Be aware that if you use a forming tap in a drill press, the hole you drill needs to be a little bigger than a hand tap drill. Off hand do not know what size that is. 7/16-20 is an odd size. Its fine thread. Coarse thread taps rule of thumb is 1.5 x diameter of tap of full threads so a 1/2-13 tap should have 1.5 inches of threads in the hole or a 1.5 inch thick plate. If you’re plate is not that thick then you would use a fine thread series tap.