A Micrometer is widely used for precise measurement of small distances. I use a Micrometer to measure the thickness in materials like sheet metal or aluminum. You can also use a Micrometer to measure the diameter of a cylindrical shape or sphere.
Types of Micrometers:
Outside micrometer, (aka micrometer caliper), typically used to measure wires, spheres, shafts and blocks[B]
Inside micrometer, used to measure the diameter of holes
Depth micrometer, measures depths of slots and steps.
This is a Starret T436XRL-9 Outside Micrometer from [url="http://www.amazon.com/Starrett-T436XRL-9-Micrometer-Ratchet-Stop-Graduation/dp/B0006J4Z6A"]Amazon[/url]
This is a Metric "Caliper" style micrometer made by “Draper.” It’s manufactured from hardened stainless steel. Slider displacements are amplified by a rack and pinion mechanism and indicated on the dial. Four way measurement: internal, external, depth and step. Reading 0.02mm. Slider has lockscrew function. Display packed in plastic storage case.