What tap or taps to use in 12 ga. (.104 inch thick) galvanized steel.
 

I need all the info I can get for hand tapping a metric 6 x .5
thread(these are very fine threads about a 1/4 inch in diameter) in
..104 inch thick galvanized steel. What is the best tap or taps? taper,
plug or bottoming? The drill I use is a .218.