Briggs & Stratton 5022621SM  Idler Pulley, 4

The purpose of the Pulley or Sheave is to ensure smooth movement of the belts within your equipment or engine. Symptoms of a bad or failing pulley could include squealing during operations and sluggish or slipping belts. If you find damage to a pulley, like metal burrs or dents, also inspect the associated shaft and bearing for similar signs of impact or abrasion. When you replace a pulley, strongly consider replacing the associated belt so that you get the maximum performance improvement.