Engineering the Guitar Capo: 200 Designs for One Purpose

A few weeks ago I bought my first guitar--which I need for a new part-time music gig-- in about 15 years. As I removed its packaging I thought about how simple most musical instruments are-for example, the guitar and most other stringed instruments are just a set of tensioned cords suspended between a nut and bridge. Stopping them with your fingers shortens the string's vibrating portion and changes the pitch, and the instrument's body naturally amplifies the vibrations caused by plucking or bowing.

My gig involves a lot of strumming and singing (folksy stuff), so I had to order a capo along with my guitar. Most seasoned guitarists are familiar with these little devices: they're used to raise the pitch of the entire guitar to play in many different keys using the same basic chord shapes. My capo's packaging spouted on and on about how it's "precision engineered" and meticulously designed, so I got to wondering about its history and design.

In a technical sense a capo is really an artificial nut (the little white notched thing close to the headstock) that's clamped to different points on the neck to change the vibrating length of all the strings at once. Because the capo can't be placed any farther up than the guitar's actual nut, it can only raise, not lower, the pitch from standard tuning. Capos are most frequently used in folk and folk-influenced music, and might have become popular in these styles because folk musicians were keen on the idea of using familiar chords in more difficult keys that better suited their voices.

All designs since the first capo came about in the mid-1700s involve some type of thin bar that depresses the strings at a preselected place and remains there by clamping onto the guitar's neck. The first device was a simple brass clip that relied on its own tension to grip the neck, but this quickly fell out of favor because the clip back scratched the heck of the neck itself. A few different late-18^th century designs that maintained tension with a screw in conjunction with a piece of wood (cejilla-style) or metal (yoke-style) solved this problem.

Three of the many capo designs (left to right): Ashborn's 1850 patent | Dunlop trigger | Planet Waves ratchet

Capo engineering really took off after the first capo patent was issued in the US in 1850, and dozens of designs have emerged since. Most of these relied on a spring or some type of screw until the development of the now-common trigger capo in 1979. This one uses a strong integral spring along with a simple clamp design (supposedly inspired by a typical clothespin) that facilitates quick one-handed changes to its position. The trigger model and a 1978 Shubb design--which uses a screw to custom-adjust the clamp to the instrument's neck width--seem to be the most popular modern devices.

A few strange capos also cropped up in the '80s. The Third Hand "partial capo" from 1980 consists of six individual "fingers" that can clamp any combination of strings, rather than all of them at once. And the ratchet capo, patented in 1989, works like a cable tie for the guitar's neck, with a lever-release for quickly changing the position.

For an instrument that's barely changed over the course of 300 years, who knew its little $15 accessory could be so complicated?

(And for those who crave more capo design info, Sterner's Capo Museum has info and images for 243 different capo types.)

Image credits: Creative Tools / CC BY 2.0 | Sterner