Greetings all; I have a sizing conundrum. I'm carving, in hard maple, on a 4 axis cnc mill, a screw to make a vise screw for a woodworking bench vise, then printing the matching nuts. The thread is a more or less buttress design 6mm pitch with a nominally 5mm tooth height. And is two start so that both halves of the half nut are identical so the screws working pitch is 12mm. I have ground the anvils of a 6" digital caliper for longer knives so I can get a diameter figure from the root of the teeth on the screw which varies a bit in order to get a clean thread. My OpenSCAD file to make the rest of the vise makes the nuts by wrapping a 7 point polygon as the tooth shape and extruding it a bit to make a thick enough profile, that is then wrapped around a cylinder, all of which is diametrically scaled to fit the individual screw to make the screw for, which is then subtracted from the fixed size blocks to make the nuts. So far, for 9 of them its been make the nuts and see if they fit, adjust the diameter of the phantom bolt if not. Is it worth the time and plastic to see if I can derive an offset from what I measure on the threaded stick, so I can make a pair of nuts that fits the individual stick on the first try? It seems to me a measurement of the root diameter should supply a diameter for the nuts by supplying the diameter of the cylinder the teeth are wrapped onto. Currently the nuts are about a day a pair in printer time. WDYT? Thanks a bunch for any advice. Cheers, Gene Heskett. -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author, 1940) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis