In order for gears of two different diameters to mesh together properly they must have the same _______________.

• A. Diametral Pitch
• B. Pressure Angle
• C. Module
• D. Diametral Pitch (Same size teeth)

Answer: (C)

Gears mesh properly when their tooth size and spacing around the pitch circle match. The module is the measure that defines that size and spacing in metric gear systems: it’s the pitch diameter divided by the number of teeth. When two gears share the same module, their teeth have consistent thickness and spacing, so you can have different diameters (and different numbers of teeth) and still get smooth, mating engagement. That’s why gears of different sizes can work together as long as the module matches.

Diametral pitch is the imperial counterpart to module, and while it serves the same purpose in its system, the question’s context points to the metric term. The pressure angle affects the shape of the tooth profile and contact quality, but it’s the module that ensures the tooth geometry aligns across gears of different diameters.