The device is designed for attaching, at least, one flexible sheet (12), usually in transparent plastics along the length of a rigid, longitudinally arched support (2), which has a cross sectional circular plan and forms the part of the framework of a glasshouse. Two principal cables (19) are fitted along the full length of the arch, around the convex side (9) of the support, on either side of the centre line (3) of the arch support. Holding loops (15) are fitted over both cables, along the length of the arch to maintain the positional relationship between the two cables. Devices (26) are fitted at the ends of each cable to provide a tension on each cable to keep them in place. The plastics sheet is inserted between the arch supports and the cables, such that when the cables are tensioned the sheet is held fixed in position.
