I badly need to change the machine heads on my 91 American standard ..It is getting harder and harder to get the guitar in tune even after tightening the keys and such..

I'm thinking on going to sprezel trim locks but i'm open for suggestions..

What i need to know is what size holes are drilled in the headstock of my 91 American standard..

Are they the regular 10mm or do the older standards have a different peghead hole size..

Thanks for any help you have to offer...

From the Fender site:

"...The diameter of the mounting hole on the headstock for our vintage style tuners is 11/32" (8.7mm), and the machines themselves have a .249" diameter string post. The mounting hole on the headstock for our die-cast tuning machines is 13/32" (10mm) with a .236 diameter string post. The modern tuning machines are obviously larger in diameter than the vintage tuners and consequently, the mounting holes will need to be enlarged to accept the new tuners...."

http://www.fender.com/support/articles/fender-guitar-tuning-machine-replacement

So, if you have the Am Std tuners (die-cast), the holes should be 13/32" (10 mm). Fender locking tuners will drop right in place of the cast tuners, and the locking tuners work very well. There are tuners that require even bigger holes, so check the new tuner specs to be sure of size.

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---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.

^^^^^^^^Thanks For the clarification^^^^^^^^^^^

I would buy a set of Fender/Schaller locking tuners. No mods would be needed. Just replace the old tuners with the new Fender/Schaller locking tuners.