Keith Richards and his 5 string guitar.

5-String – Ernie Ball Custom 5 String Set. The strings for those guitars are custom made by Ernie Ball to Keith’s exact specifications as far as gauge goes and are not for sale anywhere.

http://members.tripod.com/blue_lena/guitar2.html

In addition to being the poster child for rockers with attitude, Keith Richards is one of the greatest rhythm guitarists ever to strap on a 6-string. Or more accurately, a 5-string. Richards crafts many of his most memorable riffs using a modified open-G tuning, which involves removing his sixth string and tuning strings 5-1 to G, D, G, B, D.

“The whole idea of getting rid of the sixth string in the open tuning was having the root on the bottom,” he told GP’s Tom Wheeler in 1983. “You can get a drone going, so you have the effect of two chords playing against each other. One hangs on because you’ve just got to move one finger—or two at the most—to change the chord, so you’ve still got the other strings ringing. It’s a big sound.”

To get a handle on Richards open-G riffage, try Ex. 1, a two-bar phrase inspired by the intro to “Brown Sugar.” Bar 2 features an essential “Keef” voicing, Fadd2. An amalgam of F and C major triads, this is the grip Richards’ describes as “two chords playing against each other.”

Distilled from key moves Richards plays in “Start Me Up,” Ex. 2 revisits the interplay between C and Fadd2 we encountered in the previous example, and also includes a classic R&B pattern. This Bb5-Bb6-Bb5 shift ties Richards to his greatest hero, Chuck Berry, who used such chunky sounds to power many hits, including “Roll Over Beethoven,” “Johnny B. Goode,” and “Memphis, Tennessee.”

Open G isn’t limited to churning rhythm riffs. Spun from the country-fried licks Richards plays in the intro to “Honky Tonk Women,” Ex. 3 illustrates the tuning’s melodic side. The droning first string provides a backdrop for the twangy bends, releases, and seesaw pentatonic line.

In terms of tone, Richards favors a blend of grit and chime. “I’ve always found that a really good distortion needs to come from two different places. You want some distortion and some clarity at the same time where you need it, so I’d rather put my guitar through two amps and overload one of them.”

http://www.guitarplayer.com/article/keith-richards/Mar-05/556