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TAP DRILL SIZES AND MINOR DIAMETER CONSTANTS The size and condition of a hole before tapping has a direct bearing on the success of the tapping operation and the quality of thread produced. For best results, holes should be smooth and free of burrs. Drills should be kept sharp so that they cut freely. This is especially important in materials that work harden, such as some alloys and stainless steel. Reaming before tapping is desirable in all cases, and is a necessity for quality work, especially in the case of tapered threads. Often, the size of the hole before tapping is not clearly specified, or in many instances is specified without proper consideration of the factors involved. Misinformation on this matter can result in very high threading costs. |
