Drill Bit Size Chart
Tools
Data 2026.07.13-audit.1
Checking connection

Cutting taps · nominal 60° geometry

Tap drill,
with the assumptions visible.

Choose a target theoretical full-thread percentage, compare it with the row-level published or provisional reference, then pick a real drill. Forming taps, pipe threads, STI, ACME, and tolerance-class acceptance stay outside this calculator.

60° cutting-tap calculator FORMING / PIPE / ACME EXCLUDED
Theoretical full thread target

Scope

Nominal 60° geometry for cutting taps. It does not select a tolerance class or predict actual hole size, fit, torque, or strength.

Calculated target 1/4-20 UNC

70% theoretical drill diameter

0.2045 in
5.195 mm
Nearest listed bit 5.2 mm +0.005 mm
Published / provisional row #7 0.2010 in
Chart value calculates to 75.4% theoretical full thread
Open thread page
Axial section of 1/4-20 UNC Schematic 60-degree internal and external thread profiles with the common chart drill line and basic internal minor-diameter reference. Differences are exaggerated for explanation. BASIC INTERNAL MINOR-DIAMETER REFERENCE · 83.3% CHART DRILL Ø 0.2010 IN / 5.105 MM PITCH P = 1.270 MM 60° INTERNAL THREAD / WORKPIECE MATING EXTERNAL THREAD — BASIC PROFILE SCHEMATIC · PROFILE DIFFERENCE EXAGGERATED 75.4% THEORETICAL FULL THREAD
The 83.3% line is a basic-profile reference—not a universal interference switch. Actual fit depends on the internal and external thread profiles, class, tolerances, tap, and real hole.

2D for truth · 3D for structure

See the helix only when it helps.

The drawing above carries exact labels and prints cleanly. This optional WebGL cutaway is deliberately schematic and never loads until requested.

Optional spatial explanation SCHEMATIC · NOT TO SCALE

Why 3D is useful here

A thread is a helix, not a row of triangles.

Load a draggable cutaway to see the continuous internal thread. Exact diameter and profile comparisons remain in the 2D drawing above.

Row-level provenance

Cut-tap reference chart.

“Published” means the discrete bit was matched to a named Guhring 65% or 75% column. “Provisional” means the familiar value has not yet been closed to one audited manufacturer row.

59 Unified and metric coarse cutting-tap references
Thread Family Pitch / TPI Reference bit Diameter Calculated full thread Evidence
#1-64 UNC UNC 64 TPI #53 0.0595 in / 1.511 mm 66.5% Published 65%
#2-56 UNC UNC 56 TPI #50 0.0700 in / 1.778 mm 69.0% Provisional
#3-48 UNC UNC 48 TPI #47 0.0785 in / 1.994 mm 75.7% Provisional
#4-40 UNC UNC 40 TPI #43 0.0890 in / 2.261 mm 70.8% Provisional
#5-40 UNC UNC 40 TPI #38 0.1015 in / 2.578 mm 72.4% Provisional
#6-32 UNC UNC 32 TPI #36 0.1065 in / 2.705 mm 77.6% Published 75%
#8-32 UNC UNC 32 TPI #29 0.1360 in / 3.454 mm 69.0% Provisional
#10-24 UNC UNC 24 TPI #25 0.1495 in / 3.797 mm 74.8% Published 75%
#12-24 UNC UNC 24 TPI #16 0.1770 in / 4.496 mm 72.1% Provisional
1/4-20 UNC UNC 20 TPI #7 0.2010 in / 5.105 mm 75.4% Published 75%
5/16-18 UNC UNC 18 TPI F 0.2570 in / 6.528 mm 76.9% Published 75%
3/8-16 UNC UNC 16 TPI 5/16 0.3125 in / 7.938 mm 77.0% Published 75%
7/16-14 UNC UNC 14 TPI U 0.3680 in / 9.347 mm 74.9% Published 75%
1/2-13 UNC UNC 13 TPI 27/64 0.4219 in / 10.716 mm 78.2% Published 75%
9/16-12 UNC UNC 12 TPI 31/64 0.4844 in / 12.303 mm 72.2% Provisional
5/8-11 UNC UNC 11 TPI 17/32 0.5313 in / 13.494 mm 79.4% Provisional
3/4-10 UNC UNC 10 TPI 21/32 0.6563 in / 16.669 mm 72.2% Provisional
7/8-9 UNC UNC 9 TPI 49/64 0.7656 in / 19.447 mm 75.8% Provisional
1-8 UNC UNC 8 TPI 7/8 0.8750 in / 22.225 mm 77.0% Provisional
#0-80 UNF UNF 80 TPI 3/64 0.0469 in / 1.191 mm 80.8% Provisional
#1-72 UNF UNF 72 TPI #53 0.0595 in / 1.511 mm 74.8% Published 75%
#2-64 UNF UNF 64 TPI #50 0.0700 in / 1.778 mm 78.8% Provisional
#3-56 UNF UNF 56 TPI #45 0.0820 in / 2.083 mm 73.3% Provisional
#4-48 UNF UNF 48 TPI #42 0.0935 in / 2.375 mm 68.4% Provisional
#5-44 UNF UNF 44 TPI #38 0.1015 in / 2.578 mm 79.6% Provisional
#6-40 UNF UNF 40 TPI #33 0.1130 in / 2.870 mm 77.0% Published 75%
#8-36 UNF UNF 36 TPI #29 0.1360 in / 3.454 mm 77.6% Published 75%
#10-32 UNF UNF 32 TPI #21 0.1590 in / 4.039 mm 76.4% Published 75%
#12-28 UNF UNF 28 TPI #14 0.1820 in / 4.623 mm 73.3% Provisional
1/4-28 UNF UNF 28 TPI #3 0.2130 in / 5.410 mm 79.8% Provisional
5/16-24 UNF UNF 24 TPI I 0.2720 in / 6.909 mm 74.8% Published 75%
3/8-24 UNF UNF 24 TPI Q 0.3320 in / 8.433 mm 79.4% Provisional
7/16-20 UNF UNF 20 TPI 25/64 0.3906 in / 9.922 mm 72.2% Provisional
1/2-20 UNF UNF 20 TPI 29/64 0.4531 in / 11.509 mm 72.2% Provisional
9/16-18 UNF UNF 18 TPI 33/64 0.5156 in / 13.097 mm 65.0% Published 65%
5/8-18 UNF UNF 18 TPI 37/64 0.5781 in / 14.684 mm 65.0% Published 65%
3/4-16 UNF UNF 16 TPI 11/16 0.6875 in / 17.462 mm 77.0% Provisional
7/8-14 UNF UNF 14 TPI 13/16 0.8125 in / 20.637 mm 67.4% Published 65%
1-12 UNF UNF 12 TPI 59/64 0.9219 in / 23.416 mm 72.2% Provisional
M1 × 0.25 Metric coarse 0.25 mm 0.75 mm 0.0295 in / 0.750 mm 77.0% Provisional
M1.2 × 0.25 Metric coarse 0.25 mm 0.95 mm 0.0374 in / 0.950 mm 77.0% Provisional
M1.4 × 0.3 Metric coarse 0.3 mm 1.1 mm 0.0433 in / 1.100 mm 77.0% Provisional
M1.6 × 0.35 Metric coarse 0.35 mm 1.25 mm 0.0492 in / 1.250 mm 77.0% Published 75%
M2 × 0.4 Metric coarse 0.4 mm 1.6 mm 0.0630 in / 1.600 mm 77.0% Published 75%
M2.5 × 0.45 Metric coarse 0.45 mm 2.05 mm 0.0807 in / 2.050 mm 77.0% Provisional
M3 × 0.5 Metric coarse 0.5 mm 2.5 mm 0.0984 in / 2.500 mm 77.0% Published 75%
M3.5 × 0.6 Metric coarse 0.6 mm 2.9 mm 0.1142 in / 2.900 mm 77.0% Published 75%
M4 × 0.7 Metric coarse 0.7 mm 3.3 mm 0.1299 in / 3.300 mm 77.0% Published 75%
M5 × 0.8 Metric coarse 0.8 mm 4.2 mm 0.1654 in / 4.200 mm 77.0% Published 75%
M6 × 1 Metric coarse 1 mm 5 mm 0.1969 in / 5.000 mm 77.0% Published 75%
M8 × 1.25 Metric coarse 1.25 mm 6.8 mm 0.2677 in / 6.800 mm 73.9% Provisional
M10 × 1.5 Metric coarse 1.5 mm 8.5 mm 0.3346 in / 8.500 mm 77.0% Published 75%
M12 × 1.75 Metric coarse 1.75 mm 10.2 mm 0.4016 in / 10.200 mm 79.2% Provisional
M14 × 2 Metric coarse 2 mm 12 mm 0.4724 in / 12.000 mm 77.0% Published 75%
M16 × 2 Metric coarse 2 mm 14 mm 0.5512 in / 14.000 mm 77.0% Published 75%
M18 × 2.5 Metric coarse 2.5 mm 15.5 mm 0.6102 in / 15.500 mm 77.0% Published 75%
M20 × 2.5 Metric coarse 2.5 mm 17.5 mm 0.6890 in / 17.500 mm 77.0% Published 75%
M22 × 2.5 Metric coarse 2.5 mm 19.5 mm 0.7677 in / 19.500 mm 77.0% Published 75%
M24 × 3 Metric coarse 3 mm 21 mm 0.8268 in / 21.000 mm 77.0% Provisional

Safe use

What the equation can do.

  • Compare nominal 60° cut-thread targets.
  • Convert a real drill diameter back to theoretical full-thread percentage.
  • Show why a discrete chart bit rarely lands on an exact round percentage.

Hard boundary

What it cannot certify.

  • Forming-tap, pipe, STI, ACME, Whitworth, or wood-screw holes.
  • 2B/3B/6H fit, actual drilled-hole diameter, torque, or joint strength.
  • A substitute for the tap maker’s current chart and process control.