Forrest W Christian imach.com> writes: > I occasionally need to measure holes in circuit boards when it appears > one is out of tolerance. Mainly to be able to argue with the There are two ways to measure small holes: Hole caliper and optical comparison. The hole caliper set is a set of steel rods of different diameters, each turned down to the next lower diameter say 5mm from the end. You push the caliper into the hole to be measured starting with a good guess. The one that goes in but stops at the lip (where the turned-down-to-the-next-size edge is) is the correct one fotr the hole you are testing. This is a standard machine shop item, look at suppliers for such for a source. The optical comparison device is a specialized magnifier with a reticle that has various holes drawn on it. It is used by holding it against the part in good lighting and aligning the holes until one matches. This can also have Torx and other special tool hole markings on the slide. You can probably make your own by printing a high resolution set of circuit board 'donuts' on a transparent film (repro) slide and using it with a magnifier that has a built in transparent 'spacer'. The same tool can be used to gauge trace widths. I had a commercial one and also made my own. E.g. one of these would work: http://www.magnifierplace.com/magstore/index.html?loadfile=itemco-lt-30.html Just cut out and glue the printed slide in the lower (reticle) rectangle. Technically, this would be an optical comparator (of sorts). Peter Peter -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist