Tack strip is a building material used in most carpet installations. Laid around the perimeter of the area to be carpeted, the tack strip holds the carpet in place without messy adhesives. These fasteners are available for use over both wood and concrete subfloors. Most tack strips come in sections that are 4 feet (1.21 meters) long. The carpet strip itself is made from a thin piece of plywood, allowing the installer to cut them to the needed length easily. Gripper tacks are set into the tack strip in staggered rows at approximately a 60-degree angle. Each gripper rod also includes pre-installed fasteners, either concrete or wood nails, for attaching the strip to the appropriate subfloor. The tack strip should be oriented with the gripper tacks pointing toward the wall and approximately 3/8 inch (0.95 centimeters) of space between it and the wall. All the tack strips should be laid out before being nailed into place, a process known as a "dry fit." Following this process makes it easy to see where full strips may be used and which areas require trimmed pieces, which can cut down on waste. After the dry fit is complete, the pieces may be nailed into place with the built-in nails.