Feeler gauges are precision tools used to measure gaps or clearances between parts. They consist of a set of thin, flat metal blades, each with a specific thickness. By inserting these blades into a gap, users can determine the size of the space, which is essential in various applications, including automotive and mechanical engineering. These gauges are often used to set the clearance in engines, check the alignment of parts, and ensure proper spacing in machinery. They are available in both metric and imperial measurements, making them versatile for different industries and projects.