Aluminum series is UL listed / recognized for full trade size. This is the series of reduced wall & lightweight Flexible Metal Conduit manufactured with aluminum strip. Completely meet with UL standard. When using for electrical installation, shall refer to the regulation of NEC. The size of 5/16", is especially recommended for the wire protection in limit spaces or for light fixtures. The small size and bending radius offer advantage to satisfy the wiring environment of narrow space and corners.