在线你懂的观看网站,av免费无码不卡一区二区,孕妇变态av无码不卡顿,日韩欧精品无码视频无删节洗澡,欧美日韩亚洲综合一区二区三区,亚洲欧美中文日韩aⅴ,在线观看亚洲精品福利片,亚洲精选自拍不卡,亚洲精品国产乱码在线看天美,黑人巨茎大战欧美白妇,亚洲日韩va无码中文字幕,免费人成视频色,最新Av无码国产流畅,日本韩国三级国产,大菠萝福建app导航入口,无套av在线

A gear refers to a mechanical component with gears continuously meshing on the rim to transmit motion and power. The application of gears in transmission has been around for a long time. At the end of the 19th century, the principle of gear cutting and the emergence of specialized machine tools and cutting tools using this principle for gear cutting emerged one after another. With the development of production, the smoothness of gear operation was valued.

The Chinese name Gear appeared in the late 19th century when the foreign name Gear appeared