Metric coarse · cutting tap · nominal dimensions
M1.2 × 0.25
tap drill size.
For M1.2 × 0.25, the reference drill is 0.95 mm: 0.0374 in (0.950 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 |
|---|---|---|---|---|
| #63 | number | 0.0370 in / 0.940 mm | -0.0004 in | 80.1% |
| #62 | number | 0.0380 in / 0.965 mm | +0.0006 in | 72.3% |
| #64 | number | 0.0360 in / 0.914 mm | -0.0014 in | 87.9% |
| #61 | number | 0.0390 in / 0.991 mm | +0.0016 in | 64.5% |
| 0.9 mm | metric | 0.0354 in / 0.9 mm | -0.0020 in | 92.4% |
| 1 mm | metric | 0.0394 in / 1 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.