You'll potentially see a few different numbers. Things like 6150, ss615, etc... are the fret wire installed. 1.679 and 1.628 are the nut widths. If you look on the butt end, you may see a three digit number that was the production number. (This is NOT a serial number. Production numbers can and will cycle through more than once.) You may also see custom radius and custom back contour notes.