Standard plug is as already said a UNEF thread of 1/4 diameter X 32 threads per inch pitch. The bit used for drilling the hole for tapping 1/4-32 is a 7/32"
The Turbo plugs are ISO MF thread of 8mm diameter X .75 mm pitch
This is a excellent link to have with very good information on different threads. Good to keep in favorites for sure.
Has all the drill sizes needed when tapping threads.