sprocket
/ˈsprɒkɪt/noun
1- each of several projections on the rim of a wheel that engage with the links of a chain or with holes in film, tape, or paper链齿。
1.1
- （亦作sprocket wheel）a wheel with projections of this kind链轮。
词源
mid 16th cent. (denoting a triangular piece of timber used in a roof)： of unknown origin.