Spur Gears
Cylindrical gears with straight teeth parallel to the shaft axis. They provide simple and efficient power transmission between parallel shafts.
MOTR / GEAR — POWER TRANSMISSION REFERENCE
Industrial Gears.
Industrial gears transmit mechanical power between moving components while changing speed, torque, direction, or the axis of rotation. Gear systems are used in gearboxes, conveyors, machine tools, automation equipment, vehicles, pumps, mixers, material handling systems, and heavy machinery. Selection depends on gear type, ratio, tooth geometry, transmitted torque, rotational speed, shaft arrangement, backlash, accuracy, material, heat treatment, lubrication, mounting, alignment, noise, and expected service life.
OPERATING PRINCIPLE
Meshing teeth control mechanical power.
When two gears mesh, rotation of the driving gear causes the mating gear to rotate according to the relationship between their tooth counts and pitch geometry.
By changing gear size and arrangement, a machine can reduce speed while increasing torque, increase speed while reducing torque, reverse rotation, redirect power between shafts, or convert rotary motion into linear travel.
Reliable operation depends on accurate tooth geometry, suitable materials, proper center distance, shaft support, alignment, lubrication, and enough backlash for the operating conditions.
BASIC GEAR IDENTIFICATION
Teeth
Number of load-transmitting features around the gear.
Pitch
Tooth-spacing system used to define mating geometry.
Pitch Ø
Reference diameter used when analyzing meshing gears.
Pressure
Pressure angle associated with tooth engagement and force direction.
Ratio
Relationship between tooth counts and resulting rotational speeds.
Backlash
Controlled clearance between mating gear teeth.
SECTION / 01
Common Industrial Gear Types
Tooth orientation and shaft arrangement determine how power passes through a gear set and which loads are generated at the bearings and housings.
Helical Gears
Angled teeth engage progressively, providing smoother operation and increased tooth overlap compared with many straight-cut gear arrangements.
Bevel Gears
Conical gear forms transfer power between intersecting shafts and are frequently used to change the direction of rotational motion.
Worm Gears
A screw-like worm meshes with a worm wheel to provide substantial speed reduction within a compact right-angle arrangement.
Planetary Gears
Gear sets use a central sun gear, surrounding planet gears, and a ring gear to provide compact torque transmission and multiple possible ratios.
Rack & Pinion
A rotating pinion engages a straight toothed rack, converting rotary motion into linear movement or converting linear movement back into rotation.
Spline Gears
Multiple longitudinal teeth engage a mating internal spline to transmit torque while maintaining shaft alignment and, in some designs, allowing axial movement.
Hypoid Gears
Offset-axis gear arrangements related to bevel gearing and used where compact packaging and directional power transmission are required.
Custom Gears
Application-specific gears can use nonstandard materials, tooth forms, bores, hubs, splines, heat treatments, finishes, or precision requirements.
TOOTH / GEOMETRY
Mating gears must share compatible tooth geometry.
Matching outside diameter is not enough. Tooth pitch, pressure angle, helix geometry, center distance, and other characteristics determine whether two gears can mesh correctly.
GEAR GEOMETRY / REFERENCE TERMS
Pitch Diameter
Reference diameter representing the theoretical
rolling relationship between mating gears.
Module / Pitch
Defines tooth size and spacing using the applicable
metric or inch-based gear system.
Pressure Angle
Geometric angle that influences the direction
of transmitted tooth forces.
Helix Angle
Angle of helical teeth relative to the gear axis
and a key parameter when matching helical gears.
Center Distance
Required distance between shaft centers for the
mating gears to engage at the intended geometry.
Backlash
Clearance between mating tooth flanks that allows
lubrication, thermal movement, manufacturing
tolerance, and controlled motion.
Face Width
Tooth width across the gear face and an important
factor in load distribution and capacity.
SECTION / 02
Ratio, Torque & Performance
Gear systems are used to intentionally modify machine speed, torque, direction, and motion behavior.
Gear Ratio
Tooth-count relationships determine the relative rotational speeds of mating gears and influence the resulting torque relationship.
Torque
Tooth size, material, face width, heat treatment, geometry, and mounting determine how much mechanical load a gear can safely transmit.
Speed
High rotational speed affects tooth engagement, lubrication, balance, vibration, heat, bearing loads, and acceptable gear geometry.
Backlash
Backlash influences positioning accuracy, reversals, noise, lubrication space, thermal expansion, and the smoothness of gear engagement.
SECTION / 03
Gear Specifications
Replacement gears should be compared by complete geometry and operating requirements rather than outside diameter or tooth count alone.
Specification
What to Verify
Why It Matters
Gear Type
Spur, helical, bevel, worm, planetary, rack, or other configuration.
Determines shaft arrangement, engagement, and operating behavior.
Tooth Count
Number of teeth on each member of the gear set.
Directly influences ratio and mating geometry.
Module / Pitch
Tooth-size system and exact value.
Mating gears require corresponding tooth spacing.
Pressure Angle
Applicable pressure angle of the tooth form.
Incorrect geometry prevents proper flank contact.
Bore
Bore diameter, keyway, spline, taper, and shaft interface.
Determines mounting and torque transmission to the shaft.
Material
Steel, alloy, bronze, brass, polymer, or specialized material.
Controls strength, wear, corrosion, noise, and temperature capability.
Hardness
Heat treatment, case depth, surface hardness, or through hardness.
Influences tooth wear, contact stress, and fatigue life.
Backlash
Required operating tooth clearance.
Excessive or insufficient clearance can impair performance.
Lubrication
Oil, grease, bath, splash, circulation, or other lubrication system.
Lubrication controls friction, heat, wear, and surface damage.
SECTION / 04
Industrial Gear Selection
Begin with the required power transmission function, then establish ratio, shaft layout, load, geometry, materials, lubrication, and mounting.
01
Define the Function
Determine whether the gear set must reduce speed,
increase torque, redirect rotation, reverse direction,
synchronize shafts, or create linear motion.
02
Establish the Ratio
Determine input speed, desired output speed,
torque requirement, tooth counts, and whether
multiple reduction stages are necessary.
03
Define Shaft Geometry
Establish whether shafts are parallel, intersecting,
offset, perpendicular, or combined with a linear rack.
04
Calculate Loading
Evaluate transmitted torque, tooth forces,
shock loading, starting conditions, duty cycle,
reversals, radial forces, and thrust loads.
05
Choose Material
Select material, heat treatment, hardness, surface finish,
corrosion protection, and wear characteristics according
to the load and operating environment.
06
Verify Integration
Confirm shaft fit, center distance, bearings,
housing rigidity, lubrication, backlash, alignment,
temperature, noise, seals, and maintenance access.
Compatibility / Note 10
Matching tooth count does not make two gears interchangeable.
Replacement gears must also match the relevant pitch or module, pressure angle, helix angle and hand where applicable, face width, bore, shaft interface, center distance, material, hardness, backlash, accuracy, load capacity, and mating component geometry. A gear that appears similar can produce poor contact or rapidly damage the entire gear set if its tooth system is incorrect. See the Part Specifications, Motor & Drive Selection Guide, and Component Compatibility Guide before approving a substitution.
SECTION / 05
Industrial Gear Resources
Additional references for industrial gears, spur gears, bevel gears, worm gears, and related power-transmission components.
Industrial Gears
Broader industry resource covering gear types, manufacturing, materials, applications, specifications, maintenance, and supplier research.
Research Industrial GearsSpur Gears
Focused resource covering straight-tooth gears for parallel-shaft power transmission, applications, materials, and manufacturers.
Research Spur GearsBevel Gears
Supporting resource for conical gears used to transmit motion between intersecting shafts and change the direction of rotation.
Research Bevel GearsWorm Gears
Industry reference covering worm-and-wheel arrangements used for substantial speed reduction, torque multiplication, and right-angle power transmission.
Research Worm GearsMotors & Drives
Return to the main OpenType family reference for motors, gearing, speed control, torque transmission, actuators, and motion systems.
Motor & Drive ReferenceMotor & Drive Selection
Compare gear and drive components using torque, speed, ratio, load, mounting, controls, environment, and machine integration.
Selection Guide
Reference note:
External resources are provided for additional research
and do not establish product compatibility,
interchangeability, certification, approval, or endorsement.
Verify gear type, tooth count, module or pitch,
pressure angle, helix geometry, ratio, bore,
center distance, backlash, material, hardness,
lubrication, loading, and mounting before specifying
or replacing an industrial gear.
RELATED / DRIVES
Continue the Motor & Drive Reference
Compare gears with electric motors, controlled-motion motors, linear actuators, and the broader power-transmission system.