To calculate tapping drill size for metric threads subtract the pitch from the major diameter, Select the next larger standard drill size. Imperial UN: (Imperial Unified National thread form) A standard that describes the shape of an internal or external thread using imperial inch dimensions. Select suitable lubricant see chart below.

eg for 3/4.10 UNC pitch = 0.1, diameter = 0.75, tapping drill = 0.65 = 16.5mm. Glossary TDS: (Tap drill size) The size of the hole that must be drilled before a tapping operation. TAp mETAL OR pLAsTIc Secure workpiece and drill hole using correct size tapping drill as shown on this chart.

eg for an M5x0.75 thread the tapping drill is 5-0.75mm = 4.25mm.įor Imperial (inch) threads the tapping drill size is calculated in the same way, diameter minus pitch. As a rule of thumb, for Metric threads, the tapping drill can be calculated by subtracting the pitch from the diameter of the thread. Drill Size (inch) Pitch (TPI) Drill Size (inch) 0 - 80 3/64 1 64 0.059 (53) 72 0.059 (53) 2 56 0.067 (51) 64 0.

Un tap drill chart