Backlash in gearing refers to what?

• A. The distance between gear centers.
• B. The amount of tooth contact ratio.
• C. A small clearance between mating gear teeth that allows for lubrication and manufacturing tolerances.
• D. The gap used to compensate for thermal expansion.

Answer: (C)

Backlash is the small clearance between mating gear teeth that allows for lubrication and manufacturing tolerances. This deliberate gap prevents gears from binding as they rotate, accommodates the lubricant film, and absorbs small dimensional variations from manufacturing and assembly. It also helps handle thermal expansion and tooth deflection under load, keeping the gears operating smoothly. If the gap is too small, gears can bind or wear unevenly; if it’s too large, you get excessive play, noise, and reduced positioning accuracy. So the description that matches backlash is the tiny clearance between mating gear teeth that makes room for lubrication and manufacturing tolerances. Center distance, tooth contact ratio, and a separate thermal-expansion gap describe different concepts.