4+2 Ratio Electric Machine Heads Mini Contemporary Button (Chrome Finish) (PRN-2321-C0) - Graph Tech Guitar Labs Ltd.

4+2 Ratio Electric Machine Heads Mini Contemporary Button (Chrome Finish) (PRN-2321-C0)



RATIO® patented gear technology
RATIO® - Calibrated Machine Heads incorporate different string gauges into the tuning equation.

From Low E to High E 39:1, 24:1, 20:1, 35:1, 20:1, 12:1.

We balanced the gear ratios to each string simplifying the tuning process.

With RATIO®, a half turn is a semi-tone!

Every string reacts the same to any tuning adjustment. Predictable, precise tuning, on every string.

RATIO Machine Heads explanation video



The PRN-2321 is a right-handed set of RATIO® Calibrated Machine Heads for electric guitar that use 4 x 2 tuners.


It has a two pin casing that can be used as is, or with our Patented InvisoMatch Mounting Plates [opens in new tab].

4 different sets of InvisoMatch mounting plates in brushed aluminum are included to make installation on most guitars fast and accurate by using your existing screw mounting holes.


4x2 tuners setRatio Tuned Machine Heads: The New Standard In Tuning Technology



Gear ratio: unique for each string position - one turn-one tone
Peg holes diameter required: 13/32" (10mm)
String post diameter: 0.236" (6mm)
String post length to string hole: 0.910” (23mm)
Weight per single machine head: 0.083lbs (38g)
Weight per set of six: 0.496lbs (225g)
String diameter up to 72 gauge
Includes 6 machine heads, mounting screws and bushings
Includes complimentary 4 sets of aluminum mounting plates


Staggered Ratio Measurements.pdfRatio Installation Guide.pdfRatio Installation Guide Video


Tony Pereira

from Hamden, CT September 13, 2019

5.0 out of 5 stars

Impressive and Intuitive Upgrade

"I had to replace the vintage style tuners on a fancy, reissue guitar. The previous tuners were made to vintage specs and they kept the guitar true to form, and made it impossible to tune with any type of precision. I wasn't sure what to expect, but the reviews were consistently good, so I gave them a shot. You know when you put new strings on a guitar, and you play, and you have to continually tweak the tuning? That's where these really shine. The fact that each tuner tunes the string by the same pitch using the same twist makes tuning very intuitive and easy. I'm on board... I'm a believer."