Tapping Drill Size Calculator

The calculators below allow you to calculate the drill size required for various thread types.

The percentage of full thread required can be varied to suit, the usual range being 0.65 - 0.85.

Also included is a Pitch calculator, if you know your TPI and a TPI calculator if you have a known pitch.

BASIC HOLE SIZE CALCULATOR

Enter your Nominal Diameter and Pitch and then Press SOLVE. CLEAR ALL resets all fields.

(DRILL HOLE SIZE) = (NOMINAL DIAMETER) - (PITCH)

AMERICAN UNIFIED THREAD FORM

Enter your Outside Diameter, Percentage of Full Thread and the TPI you require and then Press SOLVE. CLEAR ALL resets all fields.

(DRILL HOLE SIZE)(") = OUTSIDE DIAMETER (") - (1.08254 X PERCENT FULL THREAD(decimal) THREADS PER INCH

AMERICAN NATIONAL THREAD FORM

Enter your Outside Diameter, Percentage of Full Thread and the TPI you require and then Press SOLVE. CLEAR ALL resets all fields.

DRILL HOLE SIZE(") = OUTSIDE DIAMETER(") - (1.299 X PERCENT FULL THREAD(decimal) THREADS PER INCH

ISO METRIC THREAD FORM

Enter your Outside Diameter, Percentage of Full Thread and the Pitch you require and then Press SOLVE. CLEAR ALL resets all fields.

DRILL HOLE SIZE(mm) = OUTSIDE DIAMETER(mm) - (1.08254) X PERCENT FULL THREAD(decimal) X PITCH(mm)

COLD FORM TAPPING (UNIFIED)

Enter your Outside Diameter, Percentage of Full Thread and the TPI you require and then Press SOLVE. CLEAR ALL resets all fields.

DRILL HOLE SIZE(inches) = OUTSIDE DIAMETER(mm) - (0.6800 X PERCENT FULL THREAD (decimal) THREADS PER INCH

COLD FORM TAPPING (METRIC)

Enter your Outside Diameter, Percentage of Full Thread and the Pitch you require and then Press SOLVE. CLEAR ALL resets all fields.

DRILL HOLE SIZE(mm) = OUTSIDE DIAMETER(mm) - (0.6800 X PERCENT FULL THREAD(decimal) X PITCH(mm)

PITCH CALCULATOR

Enter the Threads Per Inch your require, select your answer units and then Press SOLVE. CLEAR ALL resets all fields

PITCH THREADS PER INCH = /

THREADS PER INCH CALCULATOR

Enter the Pitch your require, select your units and then Press SOLVE. CLEAR ALL resets all fields

THREADS PER INCH PITCH = 1 /

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