Over at our shop, Steve has all kinds of interesting tools for measuring. This one is my favorite!

From Wiki: en.wikipedia.org/wiki/Micrometer
A micrometer (/maɪˈkrɒmɨtər/ US dict: mī·krŏm′·ĭ·tər), sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier, and digital calipers. Micrometers are similar in use to vernier calipers but are more precise although the modern digital caliper has blurred the distinction between them. A precision instrument for measuring very small distances. A typical one is the micrometer caliper. The spindle is a very accurately machined screw. It is moved by turning the ratchet knob or thimble until the object to be measured is just barely enclosed between the spindle and the anvil.