Bachi (桴, 枹) (also batchi or buchi) is the name for the straight, wooden sticks used to play Japanese taiko drums, and also (written 撥) the plectrum for stringed instruments like the shamisen and biwa.
Drum bachi are made in a wide variety of sizes and materials, as appropriate to the drum it will be used to play. A typical bachi is about 22 mm (⅞ inches) in diameter, 400 mm (16 inches) long and made out of a hardwood such as oak. These would be suitable for a wide variety of playing styles.
A bachi for playing a larger drum like the O-daiko would be bigger both in circumference and length. Similarly, smaller bachi are used for smaller drums.
Some other woods commonly used to make bachi are (Japanese names in parentheses): maple (kaede), pine (matsu), cypress (hinoki), magnolia (hou), beech (buna) and bamboo (take). Hou is one of the lightest and softest woods, most suitable for playing smaller drums with a sharp attack and less decay. On a larger drum, however, a hou bachi usually sounds "slappy" and flat, because it is too light to strike the thicker head of the drum with enough power to generate the lower tones of the drum. It is also too soft to play on the rim of the drum (in kuchi shoka, it is called a "ka") without denting the wood. Hinoki is slightly harder than hou, and is usually cheaper as well. On the opposite extreme, a kashi (oak) bachi is heavy and hard. It brings out a good sound when playing larger taikos, but on a smaller drum, it muffles the higher harmonics of the taiko, and sounds "thunky" and dead.
Taiko drumming is a highly visual art form, and so bachi are sometimes decorated with bells and/or tassels for use during performance.