Cov khoom muaj pes tsawg leeg thiab cov kev ua haujlwm tseem ceeb
Cov khoom siv muaj xws li: ib lub khib loj, cov txee, swb, sab sauv thiab sab phaj, cov khoom siv hlau, lub tog raj kheej fais fab, hydraulic systems, hluav taws xob, pneumatic systems, xws li sab laug thiab sab xis rau cov menyuam;