The parts that make up a micrometer is the frame, spindle lock lever, sleeve thimble, and ratchet knob. When fully open it measures up to three inches with each number on the sleeve equaling one tenth of an inch or to be more precise 100,000ths. The small lines break these into quarters equaling 0.025. So if we set the tool to exactly 1/2 inch with the zero on the thimble lined up with the 5 we’re now measuring half an inch or 500 thousands. If we turn it to the first line we’ve added 25 thousands and we are now reading 525 thousands. The next line would be 550 thousandths, then 575 thousands. Another turn puts us at 6/10 or precisely 600 thousands. The tool can measure even more precisely by using the gauge on the thimble as well. The numbers on the thimble represent every five thousand. If we turn the thimble one complete revolution you can see the 5, 10, 15, 20, and then finally back to 0 which gives us 25 thousandths we’re now at 625 thousands. You may have noticed the thimble also has two sets of lines a smaller line which should only be used for reference and the longer line which reads in thousands. That’s what we’ll be using for this measurement. So we’re now starting at 625 thousands.