Most guitars have one of three different string post hole sizes;
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13/32" (10mm):
- Considered the modern standard hole size used with most contemporary tuners.
- Tuning machines almost always use a bolt on nut from the front of the headstock and either a single mount screw or mount pins.
- Our Guitar Tuner Upgrade Kits for 6 Inline and 3+3 headstocks fits this style. The included UMP™ means no modifications to the instrument.
- Our standard Grip-Lock™ Open, Grip-Lock™ Closed, Classic Open and Classic Closed tuners will fit this size headstock hole
- If your guitar uses the Fender 2 Pin tuning machines, or Fender Directrofit™ upgrade kit will work perfectly on your guitar.
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11/32" (8.5mm):
- Considered the vintage standard hole size used with most pre-80's guitars and vintage reissues.
- Tuning machines have a press in bushing from the front and (usually) two screws on the back holding the machines in place. Many times, adjacent tuning machines will share a screw between them.
- Our Vintage Guitar Tuner Upgrade Kit for 6 Inline headstocks fits this style. The included UMP™ means no modifications to the instrument.
- Our Vintage Style Grip-Lock™ Tuning Machines will fit this size headstock hole.
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1/4" (6mm) with an 11/32" (8.5mm) step:
- A slightly different take on the vintage standard.
- The top of the guitar headstock has an 21/64" hole with press in bushing but the hole tapers down to 1/4" at the back.
- Unfortunately, there is no way to know whether there is a step without removing the tuning machine.
- Our Vintage Guitar Tuner Upgrade Kit for 6 Inline Headstocks will fit this style guitar IF the 1/4" portion of the hole is reamed out to 11/32".