《周礼·冬官考工记·筑氏&玉人》
制作备敲击的隧，把钟体的厚度分成六等分，用一等分作为隧凹下的深度而做成圆形。
为遂，六分其厚，以其一为之深，而圜之。
When making the chime to be struck, divide the thickness of the bell body into six equal parts, and use one part as the depth of the chime under the recess, and make it round.