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3+3 Ratio Acoustic Guitar Machine Heads (PRN-2411, 2421, Select Finish and Button Style)

3+3 Ratio Acoustic Guitar Machine Heads (PRN-2411, 2421, Select Finish and Button Style)



Regular price $114.99 USD
Regular price Sale price $114.99 USD
Sale Sold out
Select Finish
Select Button Style

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, 14:1, 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-2411 and PRN-2421 are the right-handed sets of RATIO® Calibrated Machine Heads for acoustic guitar that use 3 per side 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.


Ratio 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
Amazon Rating 5.0
Two Virginians

Reviewed in the United States on November 15, 2019

"After buying a new guitar I had some difficulty with the tuning machines. Not a lot but enough it drove me straight to the internet to find Graph Tech tuners (again). As always all the problems went away and the tuning is much more precise. Love Graph Tech."



Rated 5.0 stars
Based on 2 reviews
Total 5 star reviews: 2 Total 4 star reviews: 0 Total 3 star reviews: 0 Total 2 star reviews: 0 Total 1 star reviews: 0
100%would recommend this product
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2 reviews
  • MH
    Marvin H.
    Verified Buyer
    I recommend this product
    Rated 5 stars
    1 month ago
    Awesome tuners!

    Looks great and works great. Easy install. All around perfect product.

  • RS
    Robert S.
    Verified Buyer
    I recommend this product
    Rated 5 stars
    3 months ago
    Vast improvement over my Martin D-28’s Grovers

    I’m very pleased withe the Ratio timers. They were a breeze to install, work perfectly, and hold tune far better.

    Great product.

    Robert S

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