Cov khoom siv sib xyaw thiab cov kev ua tau zoo tseem ceeb
Cov khoom siv muaj xws li: lub khib loj, lub txee saum toj, lub swb, lub phaj sab saud thiab sab qis, cov khoom siv hlau, lub tog raj kheej fais fab, cov tshuab hydraulic, cov tshuab hluav taws xob, cov tshuab pneumatic, xws li cov menyuam sab laug thiab sab xis;