Backlash is defined as the difference between which of the following?

• A. Difference between the thickness of a tooth and the width of the tooth space
• B. Difference between center distance and gear width
• C. Difference between tooth height and width
• D. Difference between thickness of gear teeth and the width of the tooth space

Answer: (A)

Backlash is the clearance between meshing gear teeth. It’s defined by the difference between how thick a single tooth is at the pitch line and how wide the corresponding space between teeth is. This single-tooth thickness versus the tooth-space width determines the play between gears, allowing room for lubrication, thermal expansion, and manufacturing tolerances so the gears don’t bind. The other options don’t describe this specific gap between mating teeth: center distance and gear width relate to overall arrangement, tooth height and width aren’t the standard measure of play, and saying the thickness of gear teeth versus the tooth space uses plural teeth, which isn’t the typical single-tooth clearance used to quantify backlash.