Feeler Gauge Secure Tools supplies a Feeler Gauge. It is a tool used in engineering and mechanics to measure the gap between two surfaces or the thickness of a gap. It consists of a set of thin metal strips of varying thicknesses, each stamped with its measurement value. These strips can be individually selected and inserted into a gap to determine its width or the clearance between two parts. Feeler gauges come in both metric and imperial units to cater to different measurement systems. They are an essential tool for maintaining accurate tolerances and ensuring proper functionality in mechanical systems.