With the carabiner-clip end anchored to a fixed D-ring, loop or grommet, you simply feed a cord (up to 4.75mm/3/16" in diameter) through the body and pull firmly until taut. The cam-action stop mechanism locks the cord in place, holding the tension applied so the cord stays snug until you release it by lightly pressing the stop.
About 2-1/2" long, it has a spring-loaded stainless-steel carabiner closure. Available in glass-reinforced nylon or cast aluminum. A 50' hank of 2.5mm diameter cord is available separately; it has a highly reflective material woven into it for greater visibility in areas where tripping is a hazard.