Sprockets

Sprockets are the toothed wheels that connect to the shaft and mate with the chain. They are made of fabricated steel, cast steel, cast iron, or synthetic materials such as nylon. Sprockets may be of solid plate design, or be of the open design using spokes. Larger fabricated steel or cast iron sprockets mostly use the open/ spoke design to help reduce weight. with and with out hub

SPROCKET MEASUREMENTS

Number of teeth- total number of teeth around the circumference of the sprocket.

Pitch Diameter- diameter of the pitch circle that passes through the centers of the link pins as the chain is wrapped on the sprockets.

Bottom diameter - is equal to the pitch diameter minus the chain roller diameter. This dimension is used for measuring the diameter on sprockets having even numbers of teeth. 

Outside Diameter- This diameter is measured over the tips of the sprocket teeth. 

Maximum Hub and Groove Diameter- determined by the necessity for a clearance between the hub and the chain link plates when the chain is engaged with the sprocket.

SPROCKET TYPES

Sprockets are designed with four distinct hub classes and are designated Type A, B, C, D.

Type A

This type of sprocket has no hubs.

Type B 

This type have one hub protruding from one side of the sprocket. This design allows the sprocket to be fitted close to the machinery it is to be mounted on.

Type C

They have hubs extended to both sides of the sprockets plate surface. This hub design is used on the driven sprocket where  the pitch diameter is larger.

Type D

This hub has a split hub, which could be of Type B or Type C design. This design permits installation or replacement of the sprocket without disturbing shafts or bearings. The sprocket halves are held together by heavy bolts. A variation of Type D has a detachable rim that permits replacement of the tooth sections without disturbing shafts or bearings.