What’s the Difference Between a Metric Gear and an Imperial Gear?

Meet Brian Dengel at a trade show and ask him one simple question: What’s the difference between a metric gear and an Imperial gear?

That’s your ticket into a lively, insightful conversation, where gear ratios and engineering quirks come to life.

As a gearing executive at KHK USA, Dengel’s answer would be along the lines of: “Gears that use ‘module’ as the measurement for pitch are known as metric gears, whereas those that use ‘diametrical pitch’ (DP) as the pitch measurement are called Imperial gears. The difference between the two is in their length units.”

The conversation comes alive as Dengel elaborates on what distinguishes his business. For one, U.S.-based gear manufacturers make imperial gears for the most part, but KHK’s focus is on producing metric gearing, he said.

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“We are the premier supplier of metric gearing in the United States, Canada and the rest of North America,” said Dengel during an impromptu booth visit at Pack Expo Las Vegas (Sept. 29–Oct. 1, 2025). “Our current catalog contains over 27,000 configurations of stock metric gearing designed for industrial automation, packaging, equipment, robotics and other automation applications.”

Dengel brought plenty of gears to admire—from metric spur gears, helical gears and internal ring gears, to CP racks & pinions, to spiral, straight and Zerol miter gears, spiral, straight, Zerol and Hypoid bevel gears—but chose to highlight just two that he had on display: the worm-and-wheel and the right-angle drives.

Worm-and-Wheel Gears

In worm gear assemblies, a screw-like worm turns a toothed gear to produce high torque and large speed reduction in a compact form. This gearing arrangement enables precise control and is used where space is at a premium or where self-locking is required. Common applications are in hoists, conveyors and valve actuators.

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Dengel said that KHK offers the worm-in-worm wheel gears in sizes from 25 millimeters up to 400 millimeters and with speed ratios from 10:1 to 120:1.

“These are very popular items for us right now,” he noted.  

Spiral Drives and Right-Angle Gearing

Right angle drives are another popular product, according to Dengel. These drives typically utilize spiral bevel gearing, which offers smooth and efficient power transmission at 90-deg. angles.

Right-angle drives are effective in applications where high torque and quiet operation are priorities, but they are more costly to fabricate. Since the curved, angled teeth must mesh perfectly at a right angle, they are more intricate than straight-cut gears. Small deviations can cause noise, vibration or premature wear.

A Spoke in the Wheel: Tariffs

KHK USA products are manufactured in Japan—a point of pride for ensuring high-quality manufacturing and precision engineering—but Dengel noted that, in today’s climate, this commitment comes with challenges. “It is a little bit of a struggle these days because of the current situation with tariffs,” he said.

He explained that the current tariff environment has created cost pressures and logistical challenges for the company and its customers, a situation exacerbated “by the frequency of changes.”

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“The industrial automation market is used to having steady pricing, steady availability, and the fluctuation in prices is causing a real shift in the market at this time,” Dengel explained.

KHK USA is actively navigating these challenges in the shifting global landscape. “We’re navigating that situation, but it is a burden,” Dengel said.