Worm gearbox

A worm gear set consists of two parts, a worm gear and a worm wheel. The two gears are often made out of two different materials (a steel worm and a bronze worm wheel). Worm gears use a sliding action (rather than a rolling action) and transfers motion at a right angle, as illustrated in the image below.
Worm gears offer their best benefit when a large ratio is required, as a worm gear can achieve a larger total ratio with less gear sets. This means a smaller, less expensive gearbox can be used which is appealing for smaller machinery or when trying to keep installation costs low. Typically the highest ratio a worm gear set can achieve is about 100:1. Some worm gear sets cannot be back-driven which is advantageous in applications where braking is required. Worm gears can be used as a secondary locking or braking system to stop components from moving in the reverse direction.