What is a feeler blade?

A feeler blade, also known as a feeler gauge, is a tool used to measure gap widths or clearances between parts. It consists of a series of thin, flat metal blades or strips, each with a specific thickness. By inserting the appropriate blade into the gap, users can determine if the spacing falls within the desired specifications. Feelers are commonly used in automotive and mechanical applications for tasks such as valve adjustments and alignment checks.