The mallets are beaters with a rubber ball at the end. Yarn or a hard cord is wound tightly round these balls. Vibraphone mallets are usually slightly harder than the ones ones used for the marimba. They usually consist of a rubber ball core wrapped in yarn or cord and attached to a narrow dowel, most commonly made of rattan or birch (other materials, such as nylon, are sometimes used). Mallets suitable for the vibraphone are also generally suitable for the marimba. There are different ways of holding them. A common way is to hold them between the thumb and index finger, using the other fingers to help control the sticks. Playing with four mallets is harder, but allows the player to play harmony (chord with four notes).