WORM GEARBOXES COVERA HELICAL WORM GEARBOX Covera Worm Gearboxes cover the shaft distances from 80 mm to 400 mm. The standard ratios are from 5:1 to 3550:1. Other ratios and sizes are available as custom-made products. The Covera worm gear program includes one-step units, the combination gears helical-worm and double worm units. The gearbox can be delivered in foot, shaft or flange mounted options.