Parallel Key, Metric Sizes
What Is a Parallel Key?
A parallel key, also called a machine key, is a rectangular or square-section metal bar with straight, uniform sides along its full length. It's fitted into matching keyways machined into a shaft and a mating hub, such as a pulley, gear, or coupling, so that the key transmits torque between the two parts and prevents them from rotating relative to each other.
Unlike a tapered key, a parallel key has constant cross section along its length and is generally installed as a sliding or light press fit in the keyway rather than driven in at a taper. Parallel keys are widely used across general power transmission, from motors and gearboxes to conveyor drives.
Key Features and Benefits
- Uniform Cross Section: constant width and height along the full length of the key.
- Reliable Torque Transmission: transfers rotational force between shaft and hub without relying on friction alone.
- Prevents Relative Rotation: keeps shaft and hub aligned and rotating together under load.
- Simple, Field-Proven Design: widely standardized and easy to source in common sizes.
- Available in Standard Metric Sizes: matches standard metric keyway dimensions.
Materials and Finishes
- Carbon Steel: standard material for general power transmission applications.
- Plain or Bright Finish: suited to typical shop and industrial use.
Standards Compliance
- DIN 6885, Drive type fastenings without taper action, parallel keys
- ISO 773, Parallel keys and their corresponding keyways
Size Range and Availability
Available in a full metric size range matched to standard keyway dimensions, sold individually or in bulk quantities.
Related Categories and Products
Frequently Asked Questions (FAQs)
1. What is a parallel key used for?
It's used to transmit torque between a shaft and a mating hub, such as a pulley or gear, and to prevent the two parts from rotating relative to each other.
2. How is a parallel key different from a tapered key?
A parallel key has a constant cross section along its full length and typically fits as a sliding or light press fit, while a tapered key has a slight taper and is driven in to wedge the hub tight against the shaft.
3. How is a parallel key different from a Woodruff key?
A parallel key is a straight rectangular bar, while a Woodruff key is a half-moon shaped key that seats in a curved keyway, often used on smaller shafts or where the key needs to self-align.
4. What sizes are parallel keys available in?
They are available in a full metric size range matched to standard keyway dimensions.
5. What material are parallel keys made from?
They are typically made from carbon steel suited to general power transmission loads.
6. Do parallel keys need a matching keyway on both the shaft and hub?
Yes, a parallel key requires a keyway machined into both the shaft and the hub so the key can transmit torque between them.
