Armstrong 70-819 25 Piece Long Blade Gauge Set Feeler Gauges Are Mostly Used in to Measure Gap Widths - the Clearance Between Two Parts For Easy Identification, Each Blade is Permanently Marked with the Blade Thickness. Blades Are Flexible Enough That, Even If They Are All on the Same Hinge, Several Can Be Stacked Together to Gauge Intermediate Values Made in the USA - Quality and Availability