Chasen (茶筅) are bamboo whisks used to prepare matcha. They are hand-carved from a single piece of bamboo. There are differences in their style according to the type of bamboo they are made from, the shape of the tines, the number of tines, the thickness of the bamboo, the length of the bamboo, the color of the thread that is woven around the bottom of the tines, and so on. Different schools of chanoyu prefer different styles and employ different styles depending on the particular kind of tea or tea-preparation style for which it is to be used. For instance, there are specific styles for preparing thin tea (usucha), thick tea (koicha), tea offerings in tenmoku tea bowls, tea in tall cylindrical tea bowls, for including in a portable boxed tea set (chabako), for outdoor tea-making, for New Year's, and for other special auspicious occasions. Also, there are styles such as the "Rikyū-gata" (利休形) or "Sen Rikyū model"; the style attributed to Sen Rikyū's son Dōan and referred to as the "Dōan-gonomi" (道安好) style, and other such "favored" (好; konomi) styles of famous tea masters, so that the styles have continued to increase.