Cable drums are metal wheels that have grooves and are attached to the torsion pole on the far left and right side of the top of garage door. When the torsion springs turn the pole the drums will wind up the cables attached to them. The other ends of the cables are attached to the bottom left and right side of the garage door.
Garage door drum sizes
As far as drum sizes the height of the door will determine the size of the drum. The taller the door the wider the drums. This is because the taller the door the longer the cables have to be and the more cable you have the more cable has to fit on the drum. The average height of a garage door is 7 ft. tall. If your door is 8 ft. tall or less than the drums will be the same size for all. When you get over 8 ft. tall than the drums will have to be wider to hold more cable. Commercial garage doors that are 12 to 15 ft. tall will need huge drums also because the cables on these size doors need to be a lot thicker cable to lift all that weight.