![]() ![]() A good tap drill is 85% (± 2 pp) of major diameter for coarse threads, and 90% (± 2 pp) of major diameter for fine threads.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: 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. Usually thread depths of 60% to 75% are desired. Many thread sizes have several possible tap drills, because they yield threads of varying thread depth between 50% and 100%. 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. ![]() 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. ![]() 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. 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. Below is a comprehensive drill and tap size chart for all drills and taps, imperial and metric, up to 36.5 millimetres (1.44 in) in diameter. ![]()
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