For tapping with M5×0.8 tap, what size of drill will you use?

Correct option is A

To determine the correct drill size for tapping a metric thread, we use the following formula:
Drill Size = Nominal Diameter – Pitch
For an M5 × 0.8 tap:
· Nominal diameter (M5) = 5.0 mm
· Pitch = 0.8 mm
Drill Size = 5.0 − 0.8 = 4.2 mm