A capo is used to change the key of guitar without having to learn alternate chord positions or adjusting the strings with the tuning keys. The capo make it possible for a player to play in many different keys, while only knowing chord progressions in a few keys. Simply moving the capo up or down the neck raises or lowers the key. The capo can also be used to provide alternate chord voicings, for example an E chord played open on a guitar has much different tonal qualities than an e chord played with a cap on the 4th fret while playing a C chord.
A banjo capo allows the banjo player to play in many different keys while still playing rolls and patterns out of the open g-tuning. Many banjo licks and patterns to not transfer well to other chord positions, so the capo allows the player to use familiar open tuning licks. The 5-string banjo also needs a mechanism to cap the fifth string. A sliding fifth string capo is the quickest and most accurate method, but many players feel the fifth string capo gets in their way instead install spikes in the frets under which the 5th string are placed to raise the pitch.
The dobro capo allows the dobro to be played in alternate keys while letting the player play licks out of the open g-tuning position. Most dobro capos do not clamp to the neck as a guitar capo, but clamp only to the strings. Brass is the favored material for these capos allowing the instrument to resonate even while capod. The shubb dobro capo does clamp around the neck like a guitar capo.
Guitar capos come in many different shapes, sizes and even colors to meet the needs of every guitar player. The primary purpose of the guitar capo is to allow players to play in different keys while still using open-position guitar chords. An alternate use is to provide alternate voicings of the same chord. A newer development in capo designs is the partial capo which allows the player to capo only some of the strings, allowing for variants in sound.
Accomplished mandolin players do not typically used a capo and learn to play in positions as does a violin player. For beginning players; however, there are a few mandolin capos available to allow the mandolinist to play from easier open positions while playing n different keys. A banjo camp is essentially the same as a mandolin capo and in most cases will work just as well.