sprocket

A sprocket is a wheel with hard teeth evenly spaced around its circumference, designed to engage with the links of a chain or the perforations of a toothed belt. The teeth are not randomly shaped; each tooth is precisely profiled to mesh smoothly with chain pins and rollers as the sprocket rotates, converting rotational motion between shafts or changing speed and torque through gear ratio. Sprockets are fundamental to power transmission in machinery ranging from bicycles to industrial conveyors.

Sprocket geometry is standardized by pitch, which is the distance between the centers of adjacent teeth, measured in inches or millimeters. Common pitches in industrial settings include 0.5 inch, 0.625 inch, and 1 inch, each matched to corresponding chain sizes. The number of teeth on a sprocket dictates its diameter and, combined with the sprocket it meshes with, determines the speed ratio. A 20-tooth sprocket driving a 40-tooth sprocket creates a 2:1 speed reduction and a 2:1 torque increase.

Materials vary by duty. Mild steel sprockets suit general machinery; cast iron works for slower applications; hardened and ground steel teeth extend life under heavy load. Stainless steel resists corrosion in food processing and marine environments. Tooth wear is the primary failure mode: the contact surfaces deform under repeated stress, the chain begins to skip teeth, and vibration and noise increase until replacement becomes urgent.

Idler sprockets, smaller wheels with fewer teeth, are often positioned to tighten chain slack or guide the chain path without transmitting significant power. Driven sprockets receive power; driver sprockets deliver it. In multi-stage systems, a single shaft may carry multiple sprockets of different sizes to drive different chains at different ratios.

The name derives from an obsolete verb meaning to jut or project; the teeth literally project from the wheel face. Sprockets differ from gears in that they engage a chain rather than another gear; this allows misaligned shafts to transmit power with less precision in mounting, lower noise, and simpler lubrication, though with more slack and wear than gear drives. In automotive and motorcycle use, front and rear sprockets are critical to final drive ratio and fuel efficiency.