Single-direction and double-direction angular contact thrust ball bearings (Figures 1.50 and 1.51) are used for machine tool spindles requiring rigid axial guidance.
单向和双向推力角接触球轴承（图1.50和1.51）都用机床主轴轴向刚性作为指导。
3
Air propeller is the tool which transforms the power of aerial engine to the thrust of aircraft.