door roller การใช้

• A : Drill a hole through the side of one track just above one of the door rollers inside that track.
• About 1880 he patented a double-door roller sluice, suited for graving docks, and also a rolling flap-valve, used in tidal sewage outfalls.
• Inspect the door rollers to make sure they are in good condition, then check to see that the roller spindles are parallel to the door seams and are not bent.