Taps come in many different forms for many different applications and selecting the wrong style can result in wasted time, wasted money, and broken taps.
The two most commonly confused style of taps are the spiral flute (top in the above picture) and spiral point taps (bottom in the above picture). Most taps form threads by cutting them, this cutting creates metal chips that must go somewhere and where the two types of taps differ is how they deal with those chips. Spiral flute taps are designed for tapping blind holes (holes with a closed bottom) and work by pulling the chips back out of the hole so they don't clog up the tap in a hole that doesn't go all the way through. This action can be seen in the following demonstration video.
Spiral pointed taps have the front cutting edge at an forward angle to push the chips out in front as they cut. They are designed to be used in holes that go all the way through the work piece, like in horseshoes. They are also commonly called "gun taps". There cutting action and the way they push chips can be seen in the following demonstration video.
Spiral flute taps are more expensive and because they have deeper flutes to clear the chips extracting backwards, they are much more prone to breaking. They also don't have as much of a taper as a spiral point tap.
The taper on a tap is the gradual increase in size of the cutting teeth on the tap. A more taper allows the tap to self center. OSG spiral point taps are classified as plug taps and have a 6 tooth taper. Bottoming, or spiral flute taps have only 2-3 tooth tapers. There are taps called starting taps that have longer tapers but they do not have spiral points and the hole depth in a horseshoe is too short to take advantage of any tapers longer than a plug taper. The longer tapers also take longer to cut a set of threads because they have to be threaded in farther to cut full depth threads. Spiral point taps offer the ideal durability and productivity at the best price point.
We use, recommend and sell OSG TiCN coated spiral pointed plug taps. They have been the hands down winner in our own shop for performance and value.
