Gear Technology Magazine
www.geartechnology.com/articles/20954-spur-gear-fundamentals

Spur Gear Fundamentals

January 1, 1989
Gears are toothed wheels used primarily to transmit motion and power between rotating shafts. Gearing is an assembly of two or more gears. The most durable of all mechanical drives, gearing can transmit high power at efficiencies approaching 0.99 and with long service life. As precision machine elements gears must be designed.