The spark plug shaft filler ring with a thickness of 1 millimeter is an essential component for classic Citroën vehicles like the CX, DS, and HY. This ring ensures proper sealing and prevents gas or oil leakage in the spark plug shaft. It helps maintain the efficiency and performance of your engine by ensuring the correct compression. Made of durable material, it offers longevity and is specifically designed to fit seamlessly into the spark plug shaft of Citroën vehicles from these series, contributing to their historical charm and longevity.