Micrometers are used to measure outside or inside diameters. They are accurate measuring devices with precision commonly utilized to measure to the nearest one thousandth of an inch. Micrometers are available that can be used to measure to an accuracy of one ten thousandth of an inch . The outside diameter(OD)micrometer is made up of several parts, including the anvil, stirrup, spindle, sleev , thimble , internal screw, ratchet , and knurled knob. It is worth noting that the essential component is the internal screw . It has been turned to have 40 threads per inch. One divided by 40 results in 0.025 thousandth of an inch spindle movement per360┬░turn of the thimble. The micrometer may be outfitted with attachments for different application. For example, a 0.2ÔÇ?ball may be attached to the spindle to accommodate the inside radius of a pipe when measuring pipe wall thickness. Additionall, a pointed attachment may be utilized when measuring pits or very localized variations in wall thickness.