What Are DIN Standards?
DIN stands for Deutsches Institut für Normung — the German Institute for Standardization. DIN standards for drill bits define the exact dimensions, tolerances, and geometry that a drill bit must meet. They are the most widely used drill bit standards in international trade, especially for metric drill bits.
When you order drill bits by DIN number, you know exactly what you are getting — length, diameter tolerance, point angle, and shank type are all defined.
DIN 338 — Standard Length (Jobber)
DIN 338 is the most commonly produced and sold drill bit specification in the world. It defines standard-length HSS twist drill bits with straight shanks.
Key Dimensions
Diameter range — 0.5mm to 20mm
Length ratio — Approximately 10–12× the diameter (e.g., a 10mm DIN 338 bit is about 133mm overall with 87mm flute length)
Shank — Straight, cylindrical, same diameter as the cutting end
Point angle — Typically 118° or 135°
Best For
General-purpose drilling in all materials
Handheld drills and drill presses
The default choice when no specific length requirement exists
Highest availability and lowest cost per bit
Limitations
The standard length limits drilling depth. For holes deeper than about 8× the drill diameter, you need a longer bit.
DIN 340 — Long Series
DIN 340 defines long-series HSS twist drill bits with straight shanks. These are essentially stretched versions of DIN 338 bits, with longer flutes and overall length for deeper holes.
Key Dimensions
Diameter range — 2mm to 20mm
Length ratio — Approximately 15–20× the diameter (e.g., a 10mm DIN 340 bit is about 184mm overall with 121mm flute length)
Shank — Straight, cylindrical
Point angle — Typically 118° or 135°
Best For
Deep holes that exceed DIN 338 flute length
Through-holes in thick plates and blocks
Applications where the workpiece cannot be drilled from both sides
Important Considerations
Reduced rigidity — The longer body is more flexible, which can cause deflection and oversized holes. Use a drill press or CNC machine, not a handheld drill.
Peck drilling required — Always use peck drilling with long series bits to clear chips and prevent packing.
Lower cutting speeds — Reduce RPM by 10–20% compared to DIN 338 to compensate for reduced rigidity and chip evacuation challenges.
Higher cost — More material and tighter manufacturing tolerances make DIN 340 bits more expensive than DIN 338.
DIN 345 — Taper Shank
DIN 345 defines HSS twist drill bits with Morse taper shanks. These are designed for drill presses, milling machines, and other equipment with taper-accepting spindles.
Key Dimensions
Diameter range — 3mm to 100mm+
Taper — Morse taper MT1 through MT5, matched to drill diameter
Point angle — Typically 118° or 135°
Overall length — Longer than equivalent DIN 338 due to the taper shank
Best For
Large diameter drilling — 14mm and above, where straight shank chucks cannot grip reliably
Production drilling — Maximum rigidity and torque transfer for repetitive operations
Drill presses and milling machines — Equipment with Morse taper spindles
Heavy-duty applications — Structural steel, thick plate, and large-diameter through-holes
Advantages Over Straight Shank
No chuck slippage — the taper locks into the spindle under cutting force
Better concentricity — the taper self-centers in the spindle
Higher torque capacity — critical for large diameters where cutting forces are high
Quick tool changes — tap out with a drift key, insert the next size
Quick Comparison Table
DIN 338 — Straight shank, standard length, 0.5–20mm, general purpose, lowest cost
DIN 340 — Straight shank, long series, 2–20mm, deep holes, moderate cost
DIN 345 — Taper shank, standard length, 3–100mm+, heavy duty and large diameter, highest cost
Other Standards You May Encounter
DIN 1897 — Stub length (short series) straight shank bits for maximum rigidity in shallow holes
DIN 341 — Long series taper shank bits for deep, large-diameter holes
ASME B94.11M — The North American equivalent covering jobber, taper, and screw machine lengths
ISO 235 / ISO 236 — International standards that largely mirror DIN specifications
How to Specify When Ordering
When requesting a quote, always include: DIN standard number, diameter, HSS grade (M2, M35, M42), point angle (118° or 135°), and coating (bright, TiN, TiAlN, black oxide). This eliminates ambiguity and ensures you receive exactly the product you need.
