A Girth Gear, also known as a gear ring, is a large circular gear used to connect the driven shaft of a piece of machinery to the main drive shaft of the same machinery. The girth gear is typically mounted around the circumference of the machinery, often on the underside of the machinery. Girth gears are often used in rotary kilns, rotary dryers, and ball mills.

Girth gears are utilized in a variety of mining, cement, and minerals processing applications where downtime is not an option, such as copper, gold, silver, platinum, and iron ore production.