The ZipWall HDAZ12 bulk pack is the smart wayto make sure you always have zippers on hand.Best of all, you get our best zipper for less. EachZipWall Heavy Duty Zipper 12 pack contains 12self-adhesive Heavy Duty Zippers, 1 ZipWallZipper Knife and 12 sets of Door Hooks. Thisspecial knife has two blades that cut a 3/4-Inch channel from the sheeting to prevent the zipperteeth from jamming while opening and closing.Use the Heavy Duty Zipper when your barrierwill be up for a while, if there will be a lot of trafficin and out, or if the worksite will go belowfreezing. Use one zipper for a simple doorwayor place 2 zippers side by side to create awide roll-up doorway.