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Your tension strips will need to be as long as the top and bottom of your door. In some situations, your door may only have space for a tension strip along the top or bottom. After measuring the door, mark the strip at the appropriate length. Use scissors to cut your tension strips at the mark(s) you've made. For V-seal tension strips, after cutting, you'll need to fold the strip in half lengthwise, usually along some kind of a seam. Some tension strips are made from durable material, like heavy-duty plastic or metal. These kinds of strips may require tin snips to cut. Tack-fastened tension strips should be pounded into place with a hammer at the top and/or bottom of the door. These can then be opened slightly with your fingers to make a tighter seal. V-seal weather strips often have an adhesive backing. For these strips, remove the backing and press the strips into place.  Opening the V-seal will cause the strip to rise off the ground so it touches the bottom of the door when closed, improving the seal. Heavy-duty seals may be difficult to open with your hands. In situations like this, use pliers or a prying tool, like a sturdy screwdriver, to spread V-seals open.
Measure and mark the length for the strips. Cut the strips and fold them if necessary. Fasten the strips into place.