Sprocket: Definition, Types, and Terminology

What is Sprocket?

A sprocket, sprocket-wheel, or chain wheel is a profiled wheel with teeth that mesh with a chain, bar, or other perforated or notched material. The name “sprocket” applies generally to any wheel on which radial projections engage in a chain running over it.

It differs from a gear in that sprockets never mesh directly with one another, and differs from a pulley in that sprockets have teeth and pulleys are smooth, with the exception of toothed pulleys, which are used with toothed belts.

Sprockets are used in bicycles, motorcycles, tracked vehicles, and other machines to either transmit rotary motion between two shafts where gears are unsuitable or to impart linear motion to a track, tape, etc.

Perhaps the most common form of the sprocket is found in bicycles, where the pedal shaft carries a large sprocket that drives a chain, which in turn drives a small sprocket on the axle of the rear wheel. Early automobiles were also largely powered by sprocket and chain mechanisms, a practice largely copied from bicycles.

There are different types of sprockets; a maximum of efficiency is claimed for each of its originators. Sprockets usually do not have a flange. Some gears used with timing belts have flanges to keep the timing belt centered.

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Sprockets and chains are also used to transfer power from one shaft to another when slippage is not allowed, using sprockets instead of belts or ropes and sprockets instead of pulleys. They can be operated at high speed and some types of chains are designed to be silent even at high speed.

Terminology and types

Sprockets are characterized by type, which indicates hub style:

  • Type A – sprockets are flat and have no hub. They are usually mounted on flanges or hubs of the device they are driving through a series of holes that are plain or tapered.
  • Type B – sprockets have a hub on one side, allowing the sprocket to be fitted closely to the machinery on which it is mounted. This eliminates a large overhung load on the bearings of the equipment.
  • Type C – sprockets are extended on both sides of the plate and usually used on the driven sprocket where the pitch diameter is larger and where there is more weight to support on the shaft. Larger loads should have larger hubs.
  • Type D – sprockets use a type A sprocket mounted on a solid or split hub. The sprocket is split and bolted to the hub for easy removal. Speed ratio can be changed by without having to remove bearings and other equipment.

Sprocket Selection Terminology

  • Sprocket Hub Style:  A, B, and C style hub configurations are offered by many U.S. manufacturers.
  • Sprocket Caliper Diameter: The measurement from sprocket tooth valley to sprocket tooth valley on the opposite side. It measures the diameter of the sprocket plate without the teeth.
  • Sprocket Outside Diameter (OD): The measurement from sprocket tooth peak to sprocket tooth peak on the opposite side.
  • Maximum Bore Diameter: (B, C Styles) Maximum bore size a sprocket can be machined without compromising structural integrity.
  • Length Through Bore (LTB): The inside hub diameter and the length to which it was machined. The length must be able to accommodate the proper size keyway to withstand shear and torque stress.
  • Plain Bore: (B, C Styles) where inside diameter of the hub is machined with a standard keyway and two set screws.
Types of Sprockets

Types of Sprockets

1. Double Pitch Sprockets

Similar to standard sprockets except there is half the number of teeth. They are used with a small roller double pitch chain to accommodate longer distances between rollers. Common chain sizes are: 2040, 2050, 2060, 2080, and 2100 or 2042, 2052, 2062, 2082, and 2102 for larger diameters.

2. Multiple Strand Sprockets

Multi-strand sprockets are used where higher torque and power are needed, or where two or more items are being powered by a common drive shaft. Available in 40 through 160 chain pitch with plain, finished, taper-lock, or QD style hubs.

3. QD (Quick Disconnect) Sprockets

QD sprockets are used where higher working loads and high clamp loading on the shaft is desirable. They are flanged and use anchor bolts around the circumference. Sprockets with tapered bushings are easy to install and remove, provide clamp force, and align the sprocket.

4. Taper-Lock Sprockets

Taper-lock sprockets utilize a split through the taper and flange to provide a true clamp on the shaft. A Taper-Lock bushing is retained to the sprocket with set screws. They offer flexibility by allowing multiple-sized bores for a single bushing size.

5. Steel Split Sprockets

Steel split sprockets are split through the entire radius for easy installation and removal. The halves are held together by bolts. This style is available in pitch sizes 40 through 240, and bore diameters of 3/4 through 6 in.

6. Double Single Sprockets

Double single sprockets are used in applications where two or more items are powered by a common drive shaft. The space between the plates is wider than a multi-strand sprocket and allows two separate strands of chain to engage without contacting the other. One strand may exit in a different direction than the other.

7. Idler Sprockets

Idler sprockets are used where the chain may experience slack due to long lengths, where there is a non-adjustable drive shaft, or where the chain has been guided around an obstruction. Using idler sprockets prevents chain whipping and uneven load distribution.

8. Double Plus Sprockets

Double plus sprockets are specifically designed to be used with Double Plus chain and are in conveyor applications where a product is moving at twice the speed of the drive system powering the conveyor. Benefits include less noise and longer chain life.