青青青在线视频国产,韩国三级bd高清中字办公室,最近更新中文字幕2018,先锋精品一区二区三区,国产在线97色永久免费视频,欧美日韩国产精品自在自线,亚洲色精品aⅴ一区区三区,艳妇…夹得好紧,国产精品51麻豆cm传媒,久久久久久久曰本精品免费看,日本丰满护士bbw

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