Which component is typically lubricated using a Zerk fitting?

• A. A belt pulley
• B. A gear tooth
• C. A housing bolt
• D. A single bearing

Answer: (D)

Grease fittings are placed on components that need periodic, direct lubrication of a moving part. A bearing is the classic example: it has rolling elements that generate heat and wear, and a grease gun can inject lubricant into the bearing cavity through the fitting to replenish grease, flush contaminants, and keep clearance and rotation smooth.

This is why a bearing is the best answer. Belt pulleys often use sealed or pre-lubricated bearings, or their lubrication comes from a gearbox or the assembly rather than a grease fitting at the pulley itself. Gear teeth typically receive lubrication from oil or grease within a gear housing rather than a direct fitting at the tooth. Housing bolts are stationary fasteners and don’t require periodic grease through a fitting.