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

UNF · cutting tap · nominal dimensions

#3-56 UNF
tap drill size.

For #3-56 UNF, the reference drill is #45: 0.0820 in (2.083 mm).

The reference value is kept separate from the 70% and 75% calculated targets. Actual fit still depends on thread class, tool, material, runout, and the hole you really make.

Reference drill Provisional
Calibrated relative diameter · 1 in reference
Provisional reference — row-level source not closed
#45
0.0820 in · 2.083 mm
Calculates to73.3%theoretical full thread
70% target0.0828 in2.102 mm
75% target0.0816 in2.073 mm
Where this drill sits from 0 to 1 inch
#45 · 2.083 mm on a zero to 25.4 millimetre scale. Neighbor marks: 2.1 mm, #46.
0 25.4 mm
Check My Bit Box Print chart

Detail A · basic 60° profile

What the percentage describes.

“Theoretical full thread %” is radial thread height from nominal geometry. It is not axial engagement length and not a fit-class acceptance measurement.

Axial section of #3-56 UNF 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 0.0820 IN / 2.083 MM PITCH P = 0.454 MM 60° INTERNAL THREAD / WORKPIECE MATING EXTERNAL THREAD — BASIC PROFILE SCHEMATIC · PROFILE DIFFERENCE EXAGGERATED 73.3% 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.

Real drill alternatives

Neighboring sizes.

These are diameter neighbors, not silent recommendations. A positive delta makes a larger hole and a lower nominal theoretical percentage; a negative delta does the opposite.

Nearest nominal bits to #45
BitSystemDiameterDeltaCalculated full thread
2.1 mm metric 0.0827 in / 2.1 mm +0.0007 in 70.4%
#46 number 0.0810 in / 2.057 mm -0.0010 in 77.6%
2 mm metric 0.0787 in / 2 mm -0.0033 in 87.3%
#47 number 0.0785 in / 1.994 mm -0.0035 in 88.4%
5/64 fractional 5/64 in / 1.984 mm -0.0039 in 90.0%
#44 number 0.0860 in / 2.184 mm +0.0040 in 56.0%
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.

Evidence and limits

Why this row says provisional.

Tap-drill row: A familiar chart or D-minus-pitch value that was not closed against a single row in the selected OSG/Guhring public tables. Kept visible for audit, never labeled normative or manufacturer-published.

Open Drill Bit Size Chart source

60° geometry: Public primary reference for Unified and metric 60-degree thread geometry. The percentage-thread equation is a theoretical basic-profile calculation, not a fit or torque guarantee.

Open National Institute of Standards and Technology geometry source

The repository also records 11 source records and a dataset version on every page.

Nearby UNF threads

#4-48 UNF#2-64 UNF#5-44 UNF#1-72 UNF