Horse power X 240 / Diameter of wheel, ft. X Revs. per min = Strength of tooth. ...

√strength / Breath, ins. = Pitch, ins. Strength / (Pitch, ins.)2 = Breadth, ins.

The above rule will be found very suitable for a speed of circumference of about 240 feet per minute. For speeds above, add to 240 half the difference; for speeds below, deduct half the difference between 240 and the actual speed, the result being a suitable multiplier.

For instance: at 300 feet per minute, 60 being the difference, 240 / 30 = 270 multiplier.

At 160 feet per minute, 80 being the difference, 240 - 40 = 200 multiplier.

The reason being that, with higher speeds, the friction, wear, and liability to shocks is increased, at lower speeds decreased, and the teeth may advantageously be proportioned accordingly.