Metric Pitch Timing Belts

Metric pitch timing belts mate with same-pitch timing pulleys in power transmission systems where maintenance-of-speed ratio is an important design consideration. Metric pitch is the distance between belt teeth based on millimeters (mm). With metric pitch timing belts, a timing pulley transmits force to the belt via evenly-spaced grooves that mate with the teeth in the belt. These same grooves and teeth prevent belt slippage. Synchronous belt drives are highly-efficient devices. Synchronous belts come in a wide variety of materials and reinforcements. Metric pitch timing belts are also available in trapezoidal and curvilinear tooth form.

Pitch is the most important consideration when searching for metric pitch timing belts. By definition, pitch is the distance from one tooth center to the adjacent tooth center. Pitch choices for metric pitch timing belts include T pitch, AT pitch, GT pitch, HTD pitch, and super-torque pitch. T pitch is a metric trapezoidal pitch available in four pitch sizes: 2.5 mm, 5 mm, 10 mm, and 20 mm. AT pitch is a metric curvilinear pitch available in three pitch sizes: 5 mm, 10 mm and 20 mm. GT® pitch (Gates Rubber Company) is a metric curvilinear pitch from that comes in three pitch sizes: 2 mm, 3 mm and 5 mm. HTD® pitch or high torque drive pitch is a metric curvilinear pitch developed by Uniroyal (now Gates Rubber Company). HTD pitch comes in five pitch sizes: 3 mm, 5 mm, 8 mm, 14 mm, and 20 mm. Super-torque is a metric curvilinear pitch available in six sizes from 2-mm pitch to 14-mm pitch. 

When selecting metric pitch timing belts, the geometry of the belt is also important to consider. Belt width, number of teeth, and length are the most important geometric parameters. For a given pitch, a selected number of teeth will determine the belt length. Likewise, a specified belt length will determine the number of teeth for metric pitch timing belts.

Materials of construction for metric pitch timing belts include neoprene, polyurethane, rubber, and urethane. Material selection factors may include operating tension, environmental factors such as humidity and temperature, and power transmission. Many metric pitch timing belts are reinforced with fibers or cables in the tension area of the belt. Reinforcement can significantly enhance the belt’s maximum operating tension. Metallic and non-metallic reinforcement fibers are available. Common materials for reinforcement also include fiberglass, Kevlar^® (DuPont), polyester, and steel. 

Performance specifications to consider when specifying metric pitch timing belts include ultimate tensile strength, maximum operating speed, and operating temperature. The ultimate tensile strength (UTS) is the breaking strength or tension rating.  Many products are rated for a maximum operating speed, dependent on material and timing belt geometry. Some metric pitch timing belts are double-sided, truly endless, or open-ended. Double-sided belts have teeth on both sides of belt. Truly endless belts are manufactured as one closed loop; not spliced. Open-ended belts come in a roll and may be cut and spliced to the desired length and number of teeth.

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