Thermo-Cutoffs™ are designed for use when installing heat registers from underground poly ducts. They are corrugated plastic shells with a Styrofoam® spacer inside. Once in place, the concrete floor can be poured, with the spacer providing a form that prevents the shell from collapsing, and keeps dirt and dust out, the company says. When the spacer is removed, there is a correctly sized hole for floor register installation. Thermo Manufacturing, Inc., 3709 Columbus Rd. N.E., Canton, OH 44705; 888-678-3709; (Web site).