Just to add a little info that may be of help.
A product called "Rocol RTD" is used in engineering to cut threads with both taps and dies, I think it's the best product i've used for doing this as it allows a particularly smooth thread to be cut by lubricating and keeping the swarf away from the from the cutting area where the tap blades are leading into the metal. As the cut is cleaner you also get less "oversizing" on small threads which is caused by the swarf being forced between the tap and the metal you are cutting so the finished threads will have a better tolerance match to the bolts you are going to use, making a more secure fixing. For those that haven't tapped threads before, the tap should be rotated about 180deg then reversed 90deg followed by another 180deg forward and repeated until the full thread is done. This reversing forces the tap to break off the swarf into smaller parts and avoids the debris getting jammed around the cutting area.
Nigel.
