Thread strength is not directly proportional to percent of thread. In general, tap tool life can be increased significantly by using a lower percent of thread and we suggest using values between 60% and 70% for most applications.
Most tap drill charts call out only one tap drill size, and that will produce an approximate 75 percent thread. One very important factor is the drill size used to produce the hole that will be tapped. Many variables affect the performance of threaded holes and the taps used to generate them. Percentage of Thread and Tap Drill Selection:
