A concise reference table for machinists, typically provided by suppliers of small-scale machine tools and equipment, specifies the necessary drill bit sizes for creating tapped holes of various standard thread sizes. These charts often encompass both Unified National Fine (UNF) and Unified National Coarse (UNC) thread standards, as well as metric sizes. An example would show that to create a 1/4″-20 UNC tapped hole, one might need a #7 drill bit.
Such resources are essential for ensuring proper thread engagement and preventing damage to tooling or workpieces. Using the correct drill size ensures sufficient material remains for the tap to cut full threads, maximizing strength and preventing stripped threads. Historically, these charts were printed and readily available in machine shops. The digital age has brought these resources online, making them even more accessible. This easy access ensures that even hobbyists and small-scale operations can benefit from the precision engineering knowledge previously primarily held by larger manufacturers.
