They are fascinating, awe-inspiring, intriguing and beautiful. Think of circles, teeth, pressure angle, contact ratio, mating pinion, geometry, radius, circumference, mathematical curves, parabola, ellipsis, bending stress. Is your head spinning yet? Their creation requires cutting, grinding, broaching, forging, casting, extrusion, plastic and metal injection molding. Is your head aching yet? They are built into almost every machine or moveable device you use on a daily basis...bikes, refrigerators, medical equipment, sewing machines, coffee grinders, vehicles, CLOCKS. Tick-tock-tick-tock goes the clock.