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Below is a comprehensive drill and tap size chart for all drills and taps, imperial and metric, up to in diameter. In manufactured parts, holes with female screw threads are often needed; they accept male screws to facilitate the building and fastening of a finished assembly. One of the most common ways to produce such threaded holes is to drill a hole of appropriate size with a drill bit and then tap it with a tap. Each standard size of female screw thread has one or several corresponding drill bit sizes that are within the range of appropriate size—slightly larger than the minor diameter of the mating male thread, but smaller than its pitch and major diameters. Such an appropriately sized drill is called a tap drill for that size of thread, because it is a correct drill to be followed by the tap. Many thread sizes have several possible tap drills, because they yield threads of varying thread depth between 50% and 100%. Usually thread depths of 60% to 75% are desired. People frequently use a chart such as this to determine the proper tap drill for a certain thread size or the proper tap for an existing hole. ==Rules of thumb== Regarding the proportion of tap drill to thread major diameter, for standard V threads (ISO V thread and UTS V thread), there are several rules of thumb with strong predictive power: * A good tap drill is 85% (± 2 pp) of major diameter for coarse threads, and A good tap drill is 90% (± 2 pp) of major diameter for fine threads. * For metric V threads, the concept of ''major minus pitch'' (i.e., the major or widest ''diameter'' of the intended screw in millimeters minus the ''pitch'' of the threads of that screw in millimeters per thread) yields a good tap drill diameter. * * The ''major minus pitch'' technique also works for inch-based threads, but you must first calculate the pitch by converting the fraction of threads-per-inch (TPI) into a decimal. For example, a screw with a pitch of 1/20 (20 threads per inch) has a pitch of .050 and a 1/13 pitch (13 threads per inch) has a pitch of .077. Your result will only land ''near'' a tap drill size (not directly on one). * For both of these rules of thumb (85%/90% and major minus pitch), the tap drill size yielded is not necessarily the ''only'' possible one, but it is a good one for general use. * The 85%/90% rule works best in the range of 1/4"-1" (6 to 25 mm), the sizes most important on many shop floors. Some sizes outside that range have different ratios. Below, these guidelines are explored with examples. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「List of drill and tap sizes」の詳細全文を読む スポンサード リンク
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