《周礼·冬官考工记·轮人&輈人》
毂，要使它利于车轮的转动；辐，要使它直指车牙；牙，要使它牢固紧抱。
毂也者，以为利转也。辐也者，以为直指也。牙也者，以为固抱也。
The mortise must be made in a way that allows the wheel to turn freely; the spokes must be made so that they point directly towards the teeth of the wheel; the teeth must be made so that they hold firmly to the mortise.