Though fretwire comes in a variety of tang widths and barb/stud widths, the range is fairly narrow. For many years we offered our slotted boards with a .023” slot, knowing that this would accommodate all our fretwire (and most wire available elsewhere too). We recently moved up to .024”. One-thousandth of an inch isn’t much, but our customers feel that installation goes a little more smoothly with this width and there is no backbow on the fingerboards due to narrow fret slots. The .023” blades we sell with our slotting systems will normally yield a .024” slot.
Once again, there is variance in fretwire sizes, so there is no perfect slot for a particular wire. Some sizes will go in a tiny bit easier than others, but we are confident that boards slotted at .024” will serve you well. Please note that the exception is our FW75 wire. This wire is great for repair applications—for those occasions when the slots are wider after pulling frets—but many builders will use them on new instruments. If you don’t have a saw that will cut a little wider, it won’t take too much time to file the barbs a bit to help them into a standard slot.