Horizontal for 6.1 to 7.4" cylinder less top: The QUIC-STORAGE rack system holds SCBA cylinders, fire extinguishers or other cylindrical items safely and neatly. Each unit measures 7-3/4" square by 23" long and holds one cylinder. Units bolt together and may be positioned horizontally. Horizontal racks have one cradle with rubber bumper stops in the front. When one unit is placed on top of another, the bottom unit may be ordered "less top" as the bottom of the box above becomes the top for the box below it.