Our machine keys and keysteel transmit torque between a shaft and a hub. Parallel keys (DIN 6885), woodruff keys (DIN 6888), and cut-to-length keysteel bar lock pulleys, gears, and couplings to shafts, preventing rotational slip in drivetrains and machinery. Available in steel and stainless.

Machine Keys & Keysteel - Metric Sizes

What Is a Machine Key?

A machine key is a bar of metal fitted into matching slots, a keyway in the shaft and a keyseat in the hub  to lock a rotating component such as a pulley, gear, sprocket, or coupling onto a shaft. The key transmits torque between the shaft and hub, preventing the two from slipping relative to one another as power is transferred. This simple, robust method of connecting rotating parts is fundamental to virtually every drivetrain and power-transmission assembly.

At Metric Specialties we stock the principal key types. Parallel keys (DIN 6885), the most common, are rectangular or square bars that fit a straight keyway and carry high torque. Woodruff keys (DIN 6888) are semicircular and self-align in a curved seat, ideal for tapered shafts and easier assembly. A Keysteel  precision-drawn bar to the correct cross-section  is supplied for cutting keys to length on site. Available in bright mild steel and stainless, our keys and keysteel meet the tolerance and strength requirements of accurate torque transmission.

Key Features and Benefits

• Torque Transmission: Keys lock hubs to shafts, transmitting drive torque without slip in pulleys, gears, and couplings.
• Self-Aligning Woodruff Type: Semicircular woodruff keys seat and align easily, suiting tapered shafts and simpler assembly.
• Cut-to-Length Keysteel: Precision-drawn bar lets keys be cut to the exact length required on site.
• Precise Tolerances: Accurate cross-sections ensure a correct fit in standard keyways for reliable drive.
• Steel and Stainless: Bright mild steel for general drives and stainless for corrosion-resistant applications.

Materials and Finishes

• Bright Mild Steel: Standard precision-drawn keysteel and keys for general power transmission.
• High-Tensile Steel: Higher-strength keys for heavily loaded drive couplings.
• Stainless Steel: Corrosion-resistant keys for food machinery, marine, and outdoor drives.

Standards Compliance

• DIN 6885 / ISO 773  Parallel (rectangular) keys and keyways.
• DIN 6888  Woodruff keys.
• DIN 6880  Keysteel bar stock.

Common Applications and Industries

Machine keys are used throughout power transmission and rotating machinery, locking pulleys, gears, sprockets, couplings, and flywheels onto shafts in gearboxes, motors, pumps, and drivetrains. Parallel keys carry high torque in industrial machinery and vehicle transmissions, while woodruff keys suit tapered shafts and smaller drives where self-alignment and easy assembly are valued.

Across manufacturing, agriculture, marine, and general engineering, a keysteel bar lets maintenance teams cut keys to the exact size required for a repair or build. Stainless keys serve food processing, marine, and outdoor drives where corrosion resistance is essential, ensuring reliable torque transmission in demanding environments.

How to Choose the Right Key

Match the key type to the shaft and drive: a parallel key for straight keyways carrying high torque, or a woodruff key for tapered shafts and self-aligning assembly. The key cross-section is set by the shaft diameter to a standard schedule, and the length is chosen to suit the hub width and the torque to be transmitted.

Confirm the fit against the machined keyway and keyseat tolerances so the key seats snugly without excess play or forcing. Choose bright mild steel for general drives, high-tensile steel for heavily loaded couplings, or stainless for corrosion resistance, and cut the keysteel bar to length where a standard key size is not required.

Size Range and Availability

Available across parallel and woodruff keys and keysteel bar for shaft sizes from 6mm through 100mm, in bright mild steel and stainless, cut or supplied as bar.

Why Buy From Metric Specialties

As dedicated metric fastener specialists, we hold machine keys & keysteel in the sizes, grades, and finishes that engineers actually need, backed by clear DIN and ISO standard references so you can specify with confidence. Every item is sourced to recognised standards and quality-controlled, giving you consistent thread fit, strength, and corrosion performance across repeat orders.

Whether you need a single item for a repair or bulk quantities for production, our range, technical guidance, and fast dispatch help you find the exact fastener for the job. If you are unsure which size, grade, or finish suits your application, our team can help you match the right product to your load, environment, and standard, so your assemblies are reliable and built to last.

Frequently Asked Questions (FAQs)

1. What is a machine key used for?

A machine key locks a rotating component such as a pulley, gear, sprocket, or coupling onto a shaft, transmitting torque and preventing rotational slip between the shaft and hub in drivetrains and machinery.

2. What is the difference between a parallel key and a woodruff key?

A parallel key is a straight rectangular or square bar in a straight keyway carrying high torque, while a woodruff key is semicircular, self-aligning in a curved seat, and well suited to tapered shafts.

3. What is keysteel?

Keysteel is precision-drawn bar stock made to the correct key cross-section and tolerance. It is supplied so keys can be cut to the exact length needed on site for a specific shaft and hub.

4. How do I choose the right key size?

Key cross-section is determined by the shaft diameter to a standard schedule (DIN 6885), and the length is chosen to suit the hub width and torque. Match the key to the machined keyway dimensions.

5. What is a keyway and a keyseat?

A keyway is the slot machined along the shaft, and the keyseat is the matching slot in the hub. The key sits in both, bridging the shaft and hub to transmit torque between them.

6. Are machine keys available in stainless steel?

Yes. We stock stainless keys and keysteel for corrosion-resistant drives in food machinery, marine equipment, and outdoor installations.

7. Can I cut a key to length myself?

Yes. The keysteel bar is designed to be cut to length with a saw and deburred. Cutting from the bar lets you make a key to the exact hub width required for each application.

8. What is a gib-head key?

A gib-head key is a parallel or tapered key with a raised head at one end that aids removal, used where the key must be driven out for servicing. It is a variant of the standard machine key.

9. How tight should a machine key fit?

A key should fit snugly in the keyway to the specified tolerance  firm enough to transmit torque without excessive play, but not so tight that it deforms. Standard keysteel tolerances ensure the correct fit.

10. What sizes do you stock for keys and keysteel?

We stock parallel and woodruff keys and keysteel bars for shaft sizes from 6mm through 100mm, in bright mild steel and stainless.