Here's my two cents on tap selection for 2-56 threads when modding die-cast.
Tap "Tip" styles: The three most common types of tap tips or "chamfers" are:
Taper: (no picture available) The taper chamfer typically has 7 to 10 threads of taper.
Plug:The plug chamfer typically has 3 to 5 threads of taper.
Bottoming:The bottoming chamfer typically has 1 to 2 threads of taper.
I like bottoming taps as they will provide me with more thread depth in a blind hole, which means I means I don't need to drill as deeply into the posts.
The main drawback of using a bottoming tap is that it can be more difficult to start than plug or taper taps. I find that using a taper or plug tap to cut the first 2 to 3 threads then switching to a bottoming tap is an effective solution to the the starting issue.
Tap "Flute" styles:
The Straight Flute: The most common "hand tap" style is the "straight" flute. The straight flutes, while providing room for chips, do not move the chips one way or the other. In soft materials such as die-cast, they must be frequently reversed to break the chips, and/or backed out completely and cleaned so as to not jam the tap and cause it to break.
The Spiral Flute: Another flute style, more commonly used in machine tapping is the "spiral" flute. This is my preferred tap style for die-cast. The flutes on spiral flute taps are, as you might surmise, formed in a spiral around the tap. The spiral flutes evacuate the chips up and out of the hole making them especially well suited for blind holes. Because of this, they are commonly found in the “bottom” tip style.This is my current favorite for 2-56 threads in die-cast.I purchased this tap through Amazon.
Beware of "Spiral Point" taps! Spiral point taps are generally used for through holes. They have a very short spiral on the cutting face of the first few threads. This “shoots” the chips out the bottom of the hole, which is a problem when trying to tap a blind hole.