The PRB-5500 is a right-handed set of RATIO® Calibrated Machine Heads for BASS that use a 5-in-line configuration.

In order to achieve higher gear ratios, Ratio are the world's first machine heads using a double envelope gear design with a hardened steel gear. Amazingly smooth and super strong.

Headstock Configuration 5-in-line  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: 35/64" (14mm)
String post diameter: 0.547" (13.9mm)
String post length to string hole: 1.030” (26.1mm)
Weight per single machine head: 1.86oz (53g)
Weight per set of four: 9.3oz (265g)
String diameter up to 0.98 gauge (or larger if taper-wound)
Includes 5 machine heads, mounting screws, and bushings

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

From Low E to G - 36:1, 30:1, 20:1, 18:1.

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.