Machine keys and key stock are demountable machine elements that are used to transmit torque from a shaft to the component. They are usually made of steel or stainless steel and plated with zinc for wear and oxidation resistance.

The Keyseating Process

Keyseating is a machining process in which a machine key's mating internal shapes and forms are cut using a reciprocating, single-point cutting tool - similar to the shaping process. The keyseating cutter is clamped into a holder. Together with a feed bar, it is able to move vertically within a tool guide. Keyseating machines, also called keyseaters, are used primarily to cut internal keyways and other straight-sided shapes and forms in non-production parts.

Other machines used to create keyways include broaching machines, shapers, slotting machines, and milling machines. Broaching is primarily used to cut square cornered internal keyways. Milling machines can create parallel, tapered, and woodruff keyways.

Types of Machine Keys

Machine keys include many different types of keys. Variations include parallel keys, tapered keys, Woodruff keys, hi-pro keys, and non-rok keys.


  • Parallel keys are the most widely used machine key. They have a square or rectangular cross section. Rectangular faced keys are used for larger shaft diameters and square keys are used for shafts smaller than 6.5 in (170mm).
  • Tapered keys are machined with a taper along the length of the key.Tapered Keys are available with a square end or a gib end. Gib head keys are notched and tapered to tightly couple gears or pulleys with a shaft.
  • Woodruff keys are semi-circular components that can withstand great strain. They are installed deep in a shaft and firmly embedded. The main advantage of a Woodruff key is in its avoidance of the milling of a keyway near the shaft shoulders, where stress concentration already exists.
  • Hi-pro keys are similar to Woodruff keys, but lock into place. They provide superior strength and vibration resistance.
  • Non-rok keys are made of the same materials as hi-pro keys, but have shear strengths that are equivalent to those of Woodruff keys.

Types of Key Stock

There are many different types of key stock available. Choices include step, special, nonferrous, oversized, and undersized.


  • Step key stock is used with power transmission components such as couplings, gears, sheaves, sprockets and pulleys. Some products are designed for repairing damaged shafts. Others are used to mate different keyways or gears. Typically, step keystock has four dimensions (A, B, C, and D) and is available in a variety of materials and finishes.
  • Special key stock is designed for heat treating, tool making, and other engineering applications.
  • Nonferrous key stock is made from corrosion-resistant materials and designed for use in food service or marine applications. Special keystock and nonferrous keystock are specified according to height, width, length, material, finish, and quantity.
  • Oversized and undersized key stock are made slightly larger or smaller than standard keys for fitting specific applications.


Machine keys and key stock are used in all types of mechanical devices, from large factory and construction equipment to motors and parts in automobiles and small vehicles.