UNF · cutting tap · nominal dimensions
#6-40 UNF
tap drill size.
For #6-40 UNF, the reference drill is #33: 0.1130 in (2.870 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 |
|---|---|---|---|---|
| 2.9 mm | metric | 0.1142 in / 2.9 mm | +0.0012 in | 73.4% |
| #34 | number | 0.1110 in / 2.819 mm | -0.0020 in | 83.1% |
| 2.8 mm | metric | 0.1102 in / 2.8 mm | -0.0028 in | 85.5% |
| #35 | number | 0.1100 in / 2.794 mm | -0.0030 in | 86.2% |
| #32 | number | 0.1160 in / 2.946 mm | +0.0030 in | 67.7% |
| 7/64 | fractional | 7/64 in / 2.778 mm | -0.0036 in | 88.1% |
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 cross-checked.
Tap-drill row: Rows tagged with this source were matched to a named 65% or 75% cutting-tap column. The discrete drill can calculate to a slightly different percentage from nominal dimensions.
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.