metric (mm)
0.4
0.4 mm · 0.0157 in
0.4 drill bit — 0.4 mm
The 0.4 bit measures 0.4 mm (0.0157 in). The closest bits in the other series are 1/64, #40, A.
- Diameter
- 0.4 mm
- In inches
- 0.0157 in
- Cross-section
- 0.13 mm²
Closest in other series
Use this when the only bits at hand belong to another series. For tapping, prefer the slightly smaller bit over the slightly larger one — a hole can be opened up later, never closed.
One step up and down
metric (mm)
Metric bits state the millimetres outright, inch bits state sixty-fourths. Number and letter bits carry names inherited from old wire gauges, where no formula links the label to the size.
0.10.10.20.20.30.30.40.40.50.50.60.60.70.70.80.80.90.9111.21.21.251.251.41.41.61.61.81.8222.052.052.22.22.42.42.52.52.62.62.82.8333.23.23.33.33.43.43.63.63.83.8444.24.24.44.44.54.54.64.64.84.8555.25.25.45.45.55.55.65.65.85.8666.56.56.86.8777.57.5888.58.5999.59.5101010.210.210.510.5111111.511.5121212.512.51313
How to read this
- Inch bits are counted in sixty-fourths — 16/64 reduces to 1/4.
- Higher numbers are thinner; later letters are thicker, with A picking up above #1.
- An inch is 25.4 mm, so multiply the inch value by 25.4 to get millimetres.
- For tapping, drill with the bit nearest to the thread’s outside diameter minus its pitch.
Frequently asked questions
Q. How wide is the 0.4 bit?
0.4 mm, or 0.0157 inches.
Q. What would I use from another series?
The closest are 1/64 (0.397 mm), #40 (2.489 mm), A (5.944 mm).
Q. Which threads can this size tap?
None of the metric threads in this table match closely enough.
Q. What is the cross-section?
0.13 mm².