What Is A Woodruff Key?

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By Charlotte Miller

Are you curious to know what is a woodruff key? You have come to the right place as I am going to tell you everything about a woodruff key in a very simple explanation. Without further discussion let’s begin to know what is a woodruff key?

In the world of machinery and mechanical assemblies, precision and stability are paramount. To achieve this, various components work together, each with its unique role. One such unassuming yet crucial part is the Woodruff key. In this blog, we will explore the Woodruff key, its purpose, design, and how it ensures the efficient and reliable operation of machinery.

What Is A Woodruff Key?

A Woodruff key, also known as a half-moon key, is a small, semicircular metal key that is used to secure two rotating parts, typically a shaft and a hub, in mechanical assemblies. It is named after its inventor, William Woodruff, who patented this design in the 19th century.

Purpose Of A Woodruff Key

The primary purpose of a Woodruff key is to prevent relative rotational motion between a shaft and a hub while allowing them to transmit torque. By securing these two components together, it ensures that they rotate in unison, a critical requirement in many machines and devices.

Design And Installation

Woodruff keys are characterized by their unique, half-moon shape, which fits into a semicircular slot machined into the shaft or hub. The keyway on the shaft and hub corresponds to the shape of the key, ensuring a snug fit.

Here’s how a Woodruff key is typically installed:

  1. Machining: A semicircular slot, called a keyway, is machined into both the shaft and the hub, where they meet.
  2. Insertion: The Woodruff key is then inserted into the keyway on the shaft.
  3. Alignment: The hub is aligned with the shaft so that the keyway in the hub matches with the key in the shaft.
  4. Securement: The hub is slid onto the shaft, and the Woodruff key locks them together by filling the voids in the keyway and the key.
  5. Securing: A fastener, such as a nut or bolt, may be used to further secure the assembly in place.

Advantages Of Woodruff Keys

Woodruff keys offer several advantages in mechanical assemblies:

  1. Compact Design: Woodruff keys are small and occupy minimal space, making them suitable for applications with space constraints.
  2. Efficient Torque Transmission: They efficiently transmit torque from the shaft to the hub without slippage.
  3. Alignment: The key’s shape ensures that the shaft and hub are accurately aligned, preventing wobbling or misalignment.
  4. Ease of Replacement: If a key becomes damaged, it can be relatively easy to replace, ensuring the continued functionality of the assembly.

On Whatisss You Can Get To Know More Facts Like These.


Woodruff keys are used in a wide range of machinery and equipment, including:

  1. Automotive Engines: Woodruff keys are employed in various engine components, such as the camshaft, crankshaft, and timing gears.
  2. Machine Tools: They secure rotating parts in machinery, ensuring precise and synchronized movement.
  3. Transmissions: In vehicles, Woodruff keys are used in transmissions to connect gears, shafts, and other components.
  4. Agricultural Machinery: Tractors and other agricultural equipment use Woodruff keys in various applications, from power take-offs to drive systems.


While it may appear as a small and unassuming component, the Woodruff key plays a crucial role in maintaining the stability and efficiency of mechanical assemblies. Its unique design and securement method make it an ideal choice for connecting rotating parts and ensuring that they work together harmoniously. In the world of machinery and engineering, it’s often the uncelebrated components like the Woodruff key that quietly enable the smooth operation of countless devices and equipment.


What Is The Difference Between A Parallel Key And A Woodruff Key?

Parallel square and rectangular keys are normally side fitting with top clearance and are usually retained in the shaft rather, more securely than in the hub. A Woodruff Key is a half moon shaped key that is inserted into a curved slot in the shaft.

What Is The Difference Between A Sunk Key And A Woodruff Key?

Woodruff key is a type of sunk key. This key is a semicircular disc-shaped key. The thickness of the key is uniform. The shaft keyway is designed with a semicircular gap to fit the key in the Shaft.

What Is A Woodruff Key On A Crankshaft?

Putting a woodruff key on a crankshaft implies cutting a half-moon slot into the shaft with a woodruff cutter tool. The crankshaft woodruff key’s curved section would be pressed into the keyseat, while the key’s flat side interfaces with the slot in the hub, gear, or bushing.

Why Would You Use A Woodruff Key?

Woodruff keys are semi-circular discs used to connect machine parts to rotating shafts and spindles. They serve to stop gears or other machine parts from moving independently from the rotating shaft and are often installed into the recessed key seats cut into the said shafts.

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