The ZipWall HDAZ12 bulk pack is the smart way to make sure you always have zippers on hand. Best of all, you get our best zipper for less. Each heavy-duty zipper 12-pack contains 12 self-adhesive heavy-duty zippers, 1 ZipWall zipper knife and 12 sets of door hooks. This special knife has two blades that cut a 3/4" channel from the sheeting toprevent the zipper teeth from jamming while opening and closing. Use the heavy-duty Zipper when your barrier will be up for a while, if there will be a lot of traffic in and out or if the worksite will go below freezing. Use one zipper for a simple door way or place 2-zippers side by side to create a wide roll-up doorway.