bottom bracket axle（中轴）是什么意思？音标发音+图解场景

中轴 /ˈbɒtəm ˈbɹakɪt ˈaksəl/ n

English: bottom bracket axle · 中轴

释义：Tube to which the crank is attached at each end so that one end is up when the other is down.

这个词出现在以下图解场景（1）