Inch & Metric Spur Gears

SDP/SI manufactures inch spur gears in fine to medium pitches ranging from 120 to 16 pitches. We can also supply fine- to coarse-pitch metric gears from modules 0.3 through 10. Both inch and metric spur gears are available in a variety of materials, configurations, numbers of teeth, and bores. Both inch and metric gears are available in 14.5° and 20° pressure angles.

Spur gears are found in a wide variety of applications, from aerospace assemblies, medical devices, robotics, food processing, packaging, and material handling equipment to everyday products including washing machines, 3D printers, pumps, and lawn sprinklers—they're literally everywhere!

What is a Spur Gear?

A spur gear is one of the most common, economical, and efficient methods for transmitting power and motion between parallel shafts.

Spur gears are classified into two types: external and internal. External gear teeth are cut on the external surface of the cylinder form, while internal spur gears are cut on the inside of the cylindrical form (of a gear). External gears spin in opposite directions, while internal gears spin in the same direction. In general, the smaller of the two meshed gears is referred to as a pinion or pinion gear. Speed and torque can be altered by increasing or decreasing the number of teeth in the (driving) gear. Spur gears have straight teeth and mesh with other gears of the same pressure angle and (diametral) pitch; they can be part of a gear-train of two or more meshing gears.

Backlash is the “play” between gear teeth when two gears are meshed. The general purpose of backlash is to prevent gears from jamming by making contact on both sides of their teeth simultaneously. A small amount of backlash (play) is also desirable to provide for lubricant space and expansion between the gear components and the housing. For more about Gear Backlash see our technical section. (

The essential features of a gear mesh are illustrated below:

  • Center distance: the ideal distance between the centers of two external spur gears calculated for proper gear tooth meshing.
  • The pitch circle diameters (or pitch diameters): is the diameter of pitch circle.
  • Size of teeth or module (in metric).
  • Number of teeth.
  • Pressure angle of the contacting involutes: 20° pressure angle, which conforms to worldwide acceptance of this as the most versatile pressure angle.

More information can be found in our Elements of Metric Gear Technology Technical Section. (

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