When two gears mesh, they must have the same

• A. Diametral Pitch
• B. Material
• C. Surface finish
• D. Color

Answer: (A)

Two gears engage properly only if their tooth sizes and spacing line up on the same pitch circle. Diametral pitch is the measure of how many teeth fit per inch of pitch diameter, which sets that tooth size and spacing. When two gears mesh, they must share the same diametral pitch so each tooth from one gear matches the companion tooth on the other gear. If the pitches differ, the teeth won’t interlock smoothly—leading to interference, skipping, or binding—and the intended gear ratio can’t be achieved. Materials, surface finish, or color don’t affect this geometric compatibility; they influence wear, strength, or appearance, not the ability of the teeth to mesh.