Synchronous Belts

Synchronous Belts / Timing Belts

Timing belts are basically flat belts with evenly spaced teeth. They mate with complimentary teeth on a pulley or sprocket. Because there is no stretch, no slip, and no metal-to-metal contact, lubrication is unnecessary. Timing belts should be used where exact synchronization between the driver shaft and driven shaft is required.

Timing belts are much more precise than v-belts and deliver 100 percent of the intended speed with 98 percent efficiency. The trapezoidal design is sometimes referred to as an involute tooth profile. There are six standard pitch sizes in the inch system. Pitch is the distance from one tooth center to the next tooth center.

English Sizes (Inch)

English pitch timing belts are measured in inches

  • MXL (0.080″ Pitch): Mini extra light
  • XL (0.200″ Pitch): Extra light
  • L (0.375″ Pitch): Light
  • H (0.500″ Pitch): Heavy
  • XH (0.875″ Pitch): Extra heavy
  • XXH (1.250″ Pitch): Double extra heavy

Metric Sizes (Millimeter)

Metric pitch timing belts are measured in millimeters

  • T Pitch: 2.5mm, 5mm, 10mm, 20mm
  • AT Pitch: 5mm, 10mm, 20mm
  • GT Pitch (Gates®): 2mm, 3mm, 5mm
  • HTD Pitch (High Torque Drive): 3mm, 5mm, 8mm, 14mm, 20mm
  • Super-Torque: from 2mm through 14mm pitch

Trapezoidal synchronous belt specifications are found in ARPM standard IP-24 and international standards ISO 5294 and 5296.

Synchronous belts are also available with teeth on both sides (dual-sided), which are used on twisted or serpentine drives where the driven shaft rotation must be reversed from the driver shaft.

Types of Tooth Profiles

The ARPM breaks the curvilinear profiles into three primary types H-Type, S-Type, and R-Type. All have dual sided options.

H-Type (HTD)

Tooth has a round profile. Commonly available in 3mm, 5mm, 8mm, 14mm, and 20mm pitches.

S-Type (STPD)

Tooth has a circular-arc gear shape. Widely used in Europe and Asia. Use in North American is limited (but increasing due to foreign importing). Commonly available in 3mm, 4.5mm, 5mm, 8mm, and 14mm pitches.


Tooth has a deep-profile parabolic design that can be used in R-Type or H-Type sprockets. They are used in the automotive industry as cam timing drives replacing chain. Commonly available in 5mm, 8mm, 14mm, and 20mm pitches.

Helical Offset Tooth (HOT)

The teeth on the right and left halves of the belt are angled opposite each other and offset by a half a pitch. This allows the belt to self-center on the sprocket, without aiding flanges. Because of continual engagement, vibration and noise are greatly reduced.

Key Manufacturers Timing Belts / Synchronous Belts We Offer

  • Bando
  • Dodge (ABB)
  • Dayco Products
  • Gates
  • Jason Industrial
  • Mectrol (Gates)
  • TB Woods (Altra)


Content on this page was created using excerpts from the Power Transmission Handbook (5th Edition), which is written and sold by the Power Transmission Distributor’s Association (PTDA). The Power Transmission Handbook is just under 400 pages and is a valuable resource for anyone involved or interested in the power transmission industry.

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