Metric Keyway Milling — Internal Keyways to DIN 6885, ISO 773, and Metric Standards
Metric keyway applications present a specific problem for shops working primarily with inch-standard tooling: off-the-shelf inch broaches don’t cut metric keyways, metric broaches are expensive to source in North America, and the dimensional gap between metric and imperial keyway standards means improvised approaches rarely hold the right tolerance.
NMT manufactures custom keyseat millers for metric internal keyway applications — to DIN 6885, ISO 773, BS 4235, and any other metric keyway standard or custom dimension. The same one-pass milling capability that handles difficult inch-standard keyways applies equally to metric: blind bores, hard materials, short runs, non-standard bore sizes. Metric is not a special case — it’s just another set of dimensions we manufacture to.
When Metric Keyways Come Up
Metric internal keyways appear in manufacturing environments most commonly in four situations:
Imported equipment and components — European and Asian machinery, gearboxes, motors, and power transmission components are dimensioned to metric standards. When a metric hub or coupling needs a new or reworked keyway, inch broaches won’t fit and metric replacements aren’t always available off the shelf.
OEM specifications for global products — manufacturers building equipment for international markets often specify metric keyways throughout, including in components that will be machined in North American shops. The machining capability needs to match the design standard.
Metric-to-imperial shaft adaptations — when a metric shaft is adapted to mate with an inch-standard hub, or vice versa, the keyway must be cut to the shaft’s original standard. Getting this wrong means the key won’t fit or won’t transmit torque correctly.
European aerospace and defense supply chain — Airbus, Rolls-Royce, and other European primes specify metric dimensions throughout their component drawings. North American suppliers in that chain need metric keyway capability.
Metric Keyway Standards — What NMT Works To
DIN 6885 (most common metric standard): The German standard for parallel keys and keyways, widely adopted across Europe and internationally. Specifies key width, key height, shaft keyseat depth, and hub keyway depth for shaft diameters from 6mm to 500mm+. Three form variants: DIN 6885/1 (standard), DIN 6885/2 (high form), DIN 6885/3 (special). The most frequently referenced metric keyway standard in manufacturing.
ISO 773 / ISO 774: The international standard for metric rectangular and square keys. Dimensionally similar to DIN 6885/1 — most metric keyway dimensions that comply with DIN 6885 also comply with ISO 773. Used in global specifications and on drawings that reference ISO rather than DIN.
BS 4235 (British Standard): British metric keyway standard, used in UK manufacturing and on drawings from British OEMs. Dimensionally aligned with DIN 6885 for most common sizes.
JIS B 1301 (Japanese Industrial Standard): Japanese metric keyway standard, used in Japanese equipment and machinery. Dimensions are closely related to ISO 773 but have specific tolerancing conventions.
Custom metric dimensions: When the print doesn’t reference a standard — or references a proprietary OEM dimension — NMT manufactures to your exact specified dimensions regardless of whether they fall within a published standard.
DIN 6885 Metric Keyway Dimensions — Reference Table
Standard parallel key and keyway dimensions per DIN 6885/1 for common shaft diameter ranges. For machining purposes, always verify against your specific print — this table is for reference only.
| Shaft Diameter (mm) | Key Width b (mm) | Key Height h (mm) | Hub Keyway Depth t₂ (mm) |
|---|---|---|---|
| 6–8 | 2 | 2 | 1.0 |
| 8–10 | 3 | 3 | 1.4 |
| 10–12 | 4 | 4 | 1.8 |
| 12–17 | 5 | 5 | 2.3 |
| 17–22 | 6 | 6 | 2.8 |
| 22–30 | 8 | 7 | 3.3 |
| 30–38 | 10 | 8 | 3.3 |
| 38–44 | 12 | 8 | 3.3 |
| 44–50 | 14 | 9 | 3.8 |
| 50–58 | 16 | 10 | 4.3 |
| 58–65 | 18 | 11 | 4.4 |
| 65–75 | 20 | 12 | 4.9 |
| 75–85 | 22 | 14 | 5.4 |
| 85–95 | 25 | 14 | 5.4 |
| 95–110 | 28 | 16 | 6.4 |
| 110–130 | 32 | 18 | 7.4 |
Hub keyway width tolerance: Js9 (normal fit) per DIN 6885. P9 tolerance available on request for tight fit applications.
Metric Keyway Milling vs. Metric Broaching
The challenges of metric keyway broaching in a primarily inch-standard manufacturing environment are practical and immediate:
Metric broach availability in North America: Standard metric push broaches are stocked by fewer distributors than inch broaches, and the range of available bore/keyway combinations is narrower. Non-standard metric dimensions — anything outside the most common DIN 6885 sizes — typically require a custom broach with the same long lead time and high cost as a custom inch broach.
Metric blind bores: The same blind bore problem that exists for inch keyways exists for metric keyways. A metric push broach requires a relief feature at the end of the bore. If the metric hub or coupling is a blind bore — and many are — broaching requires part modification that may not be permitted.
One-off and short run economics: Metric keyways often come up as one-off repair and replacement situations — a single imported coupling that needs a new keyway, an adaptation sleeve for a retrofit application, a replacement hub for European equipment. For these applications, ordering a custom metric broach is impractical. A custom NMT keyseat miller ships in 2–3 weeks and is the correct tool for the job.
Mixed metric/imperial shops: Job shops that work predominantly in inch standards but encounter periodic metric applications can handle those applications with a custom keyseat miller on their existing equipment rather than investing in a separate metric broaching setup.
Capabilities for Metric Keyway Applications
All tooling is custom-manufactured to your metric specifications:
- Standards: DIN 6885/1, DIN 6885/2, ISO 773, BS 4235, JIS B 1301, and custom metric dimensions
- Bore diameters: Metric bore sizes from under 12mm to over 150mm — specify in millimeters
- Keyway width: Manufactured to your exact metric dimension — 2mm and up
- Keyway depth: To your print specification, in millimeters
- Tolerance: Js9 (normal fit) standard; P9 (tight fit) and D10 (loose fit) available on request
- Keyway types: Parallel (DIN 6885 form A, B, C), blind bore without relief hole, through bore, parallel/opposite
- Materials: All standard materials — mild steel, alloy steel, stainless, aluminum, bronze, titanium, and engineering alloys
- Machine compatibility: Manual drill press, manual mill, horizontal CNC, vertical CNC machining center
- Delivery: Custom metric tooling ships in 2–3 weeks
When requesting a quote for a metric application, specify dimensions in millimeters and reference the applicable standard if known. If the print uses a standard we haven’t listed, send it — we’ll manufacture to whatever the drawing calls out.
Common Metric Keyway Applications
European gearbox and motor coupling hubs — replacing or reworking keyways in metric coupling hubs from European gearbox manufacturers (SEW, Flender, Bonfiglioli, Nord, etc.). These are typically blind bores to DIN 6885 dimensions.
Imported pump and compressor components — pump impeller hubs, compressor shaft couplings, and similar rotating components from European or Asian OEMs with metric keyway specifications.
Aerospace supply chain (European primes) — metric keyways in components destined for Airbus, Safran, Rolls-Royce, and other European aerospace OEM supply chains where DIN or ISO dimensions are specified throughout.
Adaptation sleeves and shaft converters — custom sleeves that adapt metric shafts to inch equipment or vice versa, requiring a metric keyway on the metric bore side.
Food processing and packaging equipment — European food processing equipment is almost universally metric; keyway repair and replacement work on this equipment requires metric tooling.
Replacement and repair work — single-piece repair of metric hubs, couplings, and gears where the original keyway has been damaged and re-cutting in the metric dimension is required.
Ordering Metric Keyway Tooling from NMT
To quote a metric keyseat miller, we need:
- Bore diameter in millimeters
- Keyway width and depth in millimeters (from your print)
- Applicable standard (DIN 6885, ISO 773, etc.) and tolerance class if specified
- Blind or through bore
- Keyway length in millimeters
- Material and hardness
- Machine type — manual or CNC
A drawing or print of the application is the most efficient way to provide this information. We’ll confirm feasibility and quote tooling typically within one business day.
Call: 513-541-6682 Email: nationalmachinetoolco@gmail.com
National Machine Tool Co. — Cincinnati, OH — Over 100 years manufacturing custom keyseat millers, including metric applications to DIN 6885, ISO 773, and all major metric standards.