Repairing the modern automobile requires the use of many different hand and power tools. Units of measurement play a major role in tool selection. There fore, it is important to be knowledgeable about the Imperial and the metric Systems of measurement. Measuring tools must be able to measure objects to a high degree of precision. They should be handled with care at all times and cleaned before and after every use. A micrometer can be used to measure the outside diameter of shafts and the inside diameter of holes. It is calibrated in either inch or metric graduations. Telescoping gauges are designed to measure bore diameters and other clearances. They usually are used with an outside micrometer. Small hole gauges are used in the same manner as the telescoping gauge, usually to determine valve guide diameter. The screw pitch gauge provides a fast and accurate method of measuring the threads per inch (pitch) of fasteners. This is done by matching the teeth of the gauge with the fastener threads and reading the pitch directly from the leaf of the gauge,