In order to install torsion-spring hardware, we recommend a clearance of 12 in. (305 mm). On the other hand, if there is only 4 ¾ in. (121 mm) to 12 in. (304 mm) available, it is best to use a dual-track system designed for low headroom. When equipping a garage door with an electric door opener, add 2 in. (51 mm) to standard lift movements. For low-headroom system, you do not need the additional 2 in. (51 mm).   Torsion1Extension2 HeadroomOperation typeHeadroomOperation type 0″ à 4 ¾”Not possible (lower the headboard of door)0″ à 4 ¾”Not possible (lower the headboard of door) 4 ¾” à 12″   Low Headroom (double track system)4 ¾” à 8 ½”   Low Headroom (double track system) 12″ and higherStandard (12″ radius)38 ½” and higherStandard (10″ radius) Conversion: 1 in. = 25.4 mm 1. Environmental Door recommends the use of torsion springs for improved door operation and increased safety. 2. Environmental Door recommends the use of safety cables with extension springs for more security. 3. You can order a 15 inches radius with torsion springs operation. IMPORTANT: If an electric operator is being used, add 2 inches (51 mm) to headroom required to Standard lift operation.