Metric coarse · cutting tap · nominal dimensions
M1 × 0.25
tap drill size.
For M1 × 0.25, the reference drill is 0.75 mm: 0.0295 in (0.750 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 |
|---|---|---|---|---|
| #69 | number | 0.0292 in / 0.742 mm | -0.0003 in | 79.5% |
| #68 | number | 0.0310 in / 0.787 mm | +0.0015 in | 65.5% |
| #70 | number | 0.0280 in / 0.711 mm | -0.0015 in | 88.9% |
| 1/32 | fractional | 1/32 in / 0.794 mm | +0.0017 in | 63.5% |
| 0.7 mm | metric | 0.0276 in / 0.7 mm | -0.0020 in | 92.4% |
| 0.8 mm | metric | 0.0315 in / 0.8 mm | +0.0020 in | 61.6% |
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.