This self-centering jig maintains consistent 1-3/8" (35mm) hole spacing on a slotted headstock with a thickness between 1/2" (12.7mm) and 1-1/8" (28.58mm).
A drill bit for string post holes is included:
#3896 jig for classical tuners has a 13/32" (10.32mm) drill bit
#3897 jig for steel string tuners has a "G", 0.261" (6.63mm) drill bit
Line up the three holes in the jig with the hole locations you have marked on the edge of the guitar peghead. Sandwich the peghead between the two 3-1/2" x 1-1/2" (88.9mm x 38.1mm) plates of the drill jig, and clamp it in place. This automatically centers the holes on the edge of the peghead. Be sure the jig is properly located and is resting on the edge of the peghead.
If the peghead has already been slotted, we recommend making close-fitting temporary wooden spacers to fill each slot during drilling. This will help prevent splintering on the inner walls of the slots.
Wrap a bit of masking tape around the drill bit to indicate when the drilling has gone deep enough. You can use a hand drill or a drill press. Repeat the procedure on the other side of the peghead.
In normal installation, the jig will locate the holes along the centerline of each peghead edge. To drill the holes off-center, place a spacer shim between the peghead and one of the clamped aluminum plates, on the side that the hole is to be moved toward. Adjust the thickness of the shim for the desired amount of movement.