Ua ntej, yuav ua li cas rau nruab lub rooj tog tub rau khoom qhia rail 1. Ua ntej ntawm tag nrho cov, peb yuav tsum to taub cov qauv ntawm steel pob pulley slideway, uas yog muab faib ua peb qhov chaw: movable rail, nruab nrab rail thiab tsau rail. Ntawm lawv, lub txee txav tau yog lub tsheb ciav hlau sab hauv; Lub tsheb ciav hlau ruaj khov yog sab nrauv