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Obtaining Tap Drill Sizes for Thread Cutting Taps Basic Major Dia. – .0130 X % of Full Thread =Drilled Hole of Thread (inch)   Threads Per Inch Size   Example: Find drilled hole size, 1/4 - 20 with 75% thread.   .2500 - .0130 X 75 = .2010 Dia. Hole   20 (# 7 Drill)   Basic Major Dia. - % of Full Thread X mm Pitch = Drilled Hole Of thread (mm) 76.98 Size   Example: find drilled hole size, M6.0 X 1.0 tap with 70% thread. .2362 - 70 X .0393701 .2003 Dia. Hole   76.98 (5.08 mm Drill)	Obtaining Tap Drill Sizes for Thread Forming Taps Basic Major Dia. – .0068 X % of Full Thread =Drilled Hole of Thread (inch)   Threads Per Inch Size   Example: Find drilled hole size, 1/4 - 20 with 75% thread.   .2500 - .0068 X 75 = .2245 Dia. Hole   20 (5.7 mm Drill)   Basic Major Dia. - % of Full Thread X mm Pitch = Drilled Hole Of thread (mm) 147.06 Size   Example: find drilled hole size, M6.0 X 1.0 tap with 70% thread. .2362 - 70 X .0393701 .2174 Dia. Hole   147.06 (5.52 mm Drill)

Operating Formulas

Drilling Terminology The following terms and formulas can be used to determine the appropriate operating parameters. Terms       Formulas     IPM = Inches Per Minute   IPR X RPM = IPM IPR = Inches Per Revolution   IPM/RPM = IPR RPM = Revolutions Per Minute   (SFM X 3.82)/D = RPM SFM = Surface Feet Per Minute   D X RPM X .26 = SFM D = Drill Diameter         Milling Terminology The following terms and formulas can be used to determine the appropriate operating parameters. Terms       Formulas     SFM = Surface Feet Per Minute   D X RPM X .26 = SFM RPM = Revolutions Per Minute   (SFM X 3.82)/D = RPM F = Feet in Inches Per Minute   Ft X T X RPM = F Ft = Feed Per Tooth   F = Ft         T X RPM     D = Cutter Diameter         T = Number of Teeth