What -0.003 mm means on a 0.03 mm drill
The 2026-2027 product catalogue states a diameter range of 0.03 to 3.03 mm and a diameter tolerance of -0.003 mm for the DC326 solid carbide micro drill series. That wording is deliberate.
One-sided, not plus or minus
-0.003 mm means the measured cutting diameter may sit at nominal or up to 0.003 mm below it, but not above. On a hole that will be plated or fitted, an oversized drill is a scrap part; an undersized one can still be corrected or reamed.
| Nominal D1 | Acceptable measured range |
|---|---|
| 0.030 mm | 0.027 to 0.030 mm |
| 0.500 mm | 0.497 to 0.500 mm |
| 3.030 mm | 3.027 to 3.030 mm |
At the bottom of the range the tolerance is ten percent of the diameter, which is why measurement method matters as much as the number.
What the report should contain
- The measured cutting diameter for the lot, not a nominal value copied from the drawing.
- The part number and its full geometry callout.
- The carbide batch and grinding programme revision.
Ask which diameter the tolerance applies to. On a step drill there is more than one, and each stage needs its own callout.
The tolerance above is the catalogue statement for DC326. For any other series, confirm the held tolerance on the specific part number in the written quotation rather than assuming it carries across.