UNF · cutting tap · nominal dimensions
7/16-20 UNF
tap drill size.
For 7/16-20 UNF, the reference drill is 25/64: 0.3906 in (9.922 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.
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.
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.
| Bit | System | Diameter | Delta | Calculated full thread |
|---|---|---|---|---|
| 9.9 mm | metric | 0.3898 in / 9.9 mm | -0.0009 in | 73.5% |
| 10 mm | metric | 0.3937 in / 10 mm | +0.0031 in | 67.4% |
| W | letter | 0.3860 in / 9.804 mm | -0.0046 in | 79.3% |
| 9.8 mm | metric | 0.3858 in / 9.8 mm | -0.0048 in | 79.6% |
| X | letter | 0.3970 in / 10.084 mm | +0.0064 in | 62.4% |
| 10.1 mm | metric | 0.3976 in / 10.1 mm | +0.0070 in | 61.4% |
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.