TVET COLLEGE SUPPORT

KEYS AND FASTENERS

 

Type of Keys
Videos

Four main shaft keys are available: sunk key, saddle key, tangent key, and Round key. Each has different characteristics and load-bearing capabilities; hence the correct shaft key must be selected for the application based on its characteristics and benefits.

Key type Shaft key usage
Sunk keys Rectangular keys A rectangular key is generally used for shaft diameter between 1” (25 mm) and 20” (500 mm)
Generally, these have a reduced effect on the shaft due to its shallow keyway depth
Square keys A square key is used if the deeper key depth is required to transmit torque. But ensure the weakened shaft can support the load.
A square key is used for shafts diameter up to and including 1” (25 mm)Parallel sunk keys are widely available and are one of the easiest to install
Parallel sunk keys
If possible, use set screws in the hub to hold it down to stop it from sliding out during operation
Gib head keys These are very similar to rectangular/parallel keys, but it is easier to remove due to the head
Feather keys Feather keys allow the hub to move axially while transmitting the rotational torque
Woodruff keys Use it for lower loads and can accommodate any tapered shafts/hub connection.
Saddle keys Only use it for very light unidirectional loads
Tangent keys Can be used on slow bi-directional large torque applications.
Not recommended for high frequency directional change
Round / Circular Keys Used only for very low torque and speeds
It can be fitted by drilling and reaming the shaft and hub assembly together
Key diameter to be approximately sixth of the shaft diameter
 
   
Rectangular keys, as shown, are wider than their height and are sometimes called flat keys. These are used on shafts up to about 500 mm or 20″ in diameter. The extra key width allows it to transmit greater torque without increasing the depth. An increase in depth means a weaker shaft due to a reduction in effective shaft cross-sectional area.
 
Square keys are small bars of any length with similar height & width. They are inserted between a shaft and a hub to prevent relative rotation.  A square key is used if the deeper key depth is required to transmit torque. But ensure the weakened shaft can support the load.
 
Parallel keys are a critical component used to efficiently convey shaft rotation to gears. These items are used in machine tools, automobiles, construction equipment, food machinery, pumps, and more. Parallel shaft keys come in different names depending on the vendor and industry in which they are used. They are variously referred to as parallel shaft keys, machine keys, and shaft keys, but these all refer to the same product.
These items are used in machine tools, automobiles, construction equipment, food machinery, pumps, and more.
 
Gib head sunk keys are very similar to rectangular/parallel keys, but it is easier to remove due to the head
 
Feather Key is a rectangular key that connects the keyways of a gear, pulley, or shaft's hub to another keyway. It's permanently fixed in one keyway and can slide freely in the other, allowing the shaft to drive the hub or be driven by it at various positions along the shaft. Feather keys are also known as spline keys
 
Woodruff keys, also known as half-moon keys, are semi-circular discs that are used to connect machine parts to rotating shafts and spindles. They are inserted into key seats that are created by a woodruff key cutter or arbor cutter. The key prevents gears, hubs, or other components from moving independently of the shaft or spindle. Woodruff keys are often installed into recessed key seats cut into the shafts.
 
A saddle key is a type of shaft key that is installed on the surface of a machine shaft and fits into a keyway in the shaft. Saddle keys are concave and grip the shaft by friction, resisting relative motion and transmitting torque.
 
Tangent keys are a pair of rectangular keys that are placed at right angles to each other on the shaft, and tangent to the shaft's surface. Each key can only withstand torsion in one direction. Tangent keys are used in large, heavy-duty shafts.
 
 
Round keys, also known as pin keys, Scotch keys, or Dutch keys, are cylindrical keys that fit into holes drilled partly in the shaft and partly in the hub. They are available in both inch and metric sizes and are offered in carbon steel and stainless steel.