Types of Keys

Keys are machine elements used to removably join machine parts such as gears, pulleys, and couplings to shafts.They act as the medium that transfers rotary motion from the shaft to the machine part mounted on it.

Keys are made in various shapes and with various properties depending on where they will be used. We can list the types of keys as follows:

TRANSVERSE (CROSS) KEYS	LONGITUDINAL (PARALLEL) KEYS
Single-taper transverse keys	Tapered (drive-fit) keys
Double-taper transverse keys	a) Plain (flat) key b) Gib-head key c) Tangent key d) Woodruff key
	Untapered (parallel/sliding-fit) keys
	a) Woodruff keys
	b)Tangent keys
	c)Splined shafts

TRANSVERSE (CROSS) KEYS

These are keys fitted perpendicular to the shaft axis. Rather than joining parts together, these keys are mainly used to resist transverse loads and for adjustment purposes. They are also used where parts need to be removed and refitted frequently.

For this type of key, plain carbon steels with a tensile strength of 60 N/mm² are used.

In transverse keys, the taper of the key varies depending on the working conditions.
Where the connection doesn’t need to be dismantled often (for adjustment purposes): 1:5  to 1:10
Where it is meant to come loose on its own, it’s made 1:15 to 1:25.
For tight (rigid) joints, 1:30 to 1:40

In transverse keys, the key thickness is between 1:3  and 1:4 of the shaft diameter.

LONGITUDINAL (PARALLEL) KEYS

Longitudinal keys are keys that run parallel to the shaft axis. There are two kinds: tapered (drive-fit) keys and untapered (parallel/sliding-fit) keys.

In tapered keys, a taper of 1:100 is given to the top surface of the key and the groove cut in the hub. This taper creates the clamping action by wedging the shaft and hub apart.

Longitudinal keys are generally made from plain carbon steel (grade ç1060), or, on request, from heat-treated (quenched-and-tempered) steel or case-hardening steel. They are sold on the market under the name “key steel.”

Key steels up to 25 mm have a tensile strength of 50 N/mm², while those above 25 mm have a tensile strength of 60 N/mm². Key steels are manufactured straight, bright-finished, and to precise dimensions, in square, rectangular, and flat rectangular cross-sections

How Longitudinal Keys Are Designated per the Turkish Standard (TSE)
When ordering longitudinal keys, the key name, dimensions, and TS number are specified. For example, the designation for a gib-head key with width b = 16, height h = 10, and length l = 180 mm is: Gib-head key 16x10x180 TS147/6

Tapered (Drive-Fit) Keys

In tapered keys, a taper of 1:100 is given to the top surface of the key and the groove cut in the hub. This taper creates the clamping action by wedging the shaft and hub apart.

Untapered Keys (Parallel/Sliding-Fit Keys)

Parallel/sliding-fit keys serve to transmit and resist forces applied to their side faces. They function as fitting or sliding keys. There is a gap between the top surface of the key and the hub. It is fitted tightly into the shaft keyway.

Woodruff Key

Shaped like a half-moon, it is fitted into a matching half-moon-shaped groove cut in the shaft. Keyways for these are cut with special (T) milling cutters. This is a type of key widely used in machine construction, machine tools, and pump shafts. They are made from steels with a tensile strength of 50 kg/mm².

Tangent Keys

Used for transmitting large forces. Used for shaft-and-hub connections with diameters greater than 60 mm, in places with very large torques, impact loads, and similar conditions.

Tangent keys have a taper of 1:100, and during assembly, a pair of tangent keys offset by 120° is used. If a difficulty is encountered, the offset between the keys can be taken as 180°.

Splined Shafts 147/14-18 

Used for transmitting large torques and large amounts of power, in motor vehicles, in heavily loaded gearboxes, and similar applications. They work by allowing movement along the shaft axis.

For detailed information, see:
What Is a Splined Shaft? Where Is It Used
How Is a Splined Shaft Made?

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