To mesh two gears of different diameters, they must have the same

• A. Number of teeth
• B. Face width
• C. Diametral Pitch
• D. Addendum length

Answer: (C)

When gears mesh properly, their teeth must have the same size and spacing along the pitch circle. That spacing and size is defined by the diametral pitch. Diametral pitch is the number of teeth per inch of pitch diameter, which sets how thick each tooth is and how far apart the teeth are as they engage. If two gears share the same diametral pitch, a larger gear can have more teeth but the teeth still fit together because the tooth profiles are compatible. If the diametral pitch differed, the teeth wouldn’t mesh correctly, leading to interference or gaps.

Face width affects how wide the gears are along the shaft and doesn’t determine meshing compatibility. Addendum length relates to tooth height and is tied to the pitch, but it’s the matching tooth size and spacing (diametral pitch) that truly governs whether gears of different diameters will mesh smoothly.