The Park Tool CC-3.2 Chain Checker is an essential tool for maintaining optimal bike performance. It accurately indicates when a chain reaches 0.5% and 0.75% wear, which are the points most manufacturers recommend for replacement to prevent poor shifting and costly damage to the derailleur and rear cogs. This precise gauge features permanent measurement markings and is compatible with most derailleur chains from 5 to 12-speed. For 5-to-10-speed chains, replace at or before 0.75% wear. For 11-to-12-speed chains, replace at or before 0.5% wear.