Feem ntau yog siv rau cov phab ntsa drilling xws li cib, thaiv, abrasive qhob thiab cov pob zeb muaj zog.
Qhov zoo tshaj plaws, tshem tawm plua plav zoo dua, ceev ceev thiab lub neej ntev.
Qhov ntev thiab xov tuaj yeem muab tau raws li qhov kev thov.