There are four basic design features that are incorporated into the design of all cutting tools, including taps. They include cutting face (hook), relief, base material, and surface treatment or coating. We will begin this series of tips with hook and relief.

The cutting face is that portion of the tap flute, between the major and minor diameter of the thread, that cuts or shears the workpiece material. The entry angle of the cutting face into the workpiece material is measured in degrees, from positive to negative, from a perpendicular reference line through the axis of the tool.

Positive hooks are used for soft materials that produce continuous (stringy) chips such are aluminum, mild steel, and stainless. Due to the positive angle, the cutting faces are fragile and may chip easily. Negative hooks are used for materials producing broken or powder chips, or those that have been hardened. This type of cutting face is much stronger and is also less prone to chipping.

Relief on a tap may be found on the chamfer's major diameter (required for tapping), or in the threads, in the form of radial clearance or back taper. Radial or thread relief is a thinning of the tooth from the cutting face to the heel to relieve cutting pressures and friction across the land of the tap. Thread relief is applied for materials that are tough, hard, or have high elastic memory (shrinks or squeezes the tap creating friction). Back taper is the reduction of the major, pitch, and minor diameters from the first thread at the front of the tap to the last thread near the shank. While thread relief is applied for specific applications, back taper is applied to all taps.

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