Thickness gages are used for checking and measuring small openings , such as contact point clearances, narrow slots, etc. these gages are made in many shapes and sizes, and , thickness gages can be made with multiple blades (usually 2 to 26). Each blade is a specific number of thousandths of an inch thick. This enables the application of one tool to the measurement of a variety of thickness .some thickness gage blades are straight, whereas others are bent at 45- and 90-degree angles at the end. Thickness gages can also be grouped so that there are several short and several long blades together. Before using a feeler gage, remove any foreign matter from the blades. You cannot get a correct measurement unless the blades are clean.