Oxford English Dictionary. Oxford University Press. 1989. A wheel with a groove round its rim, a sheave. A wheel or drum fixed on a shaft and turned by a belt, cable, etc.,
Prater, Edward L. (1994), Basic Machines (页面存档备份,存于互联网档案馆), Naval Education and Training Professional Development and Technology Center, NAVEDTRA 14037
Prater, Edward L. (1994), Basic Machines (页面存档备份,存于互联网档案馆), Naval Education and Training Professional Development and Technology Center, NAVEDTRA 14037