This system is the most popular available, with the welded product widely used by almost all unit manufacturers. The profiles are assembled using nylon keys and are available in 18×8 and 25×8 sizes in a range of solid colours and woodgrain foils. The painted profiles can be bent but joints between overlapping arches must be at 90°. The extruded version of the profile ensures complete symmetry of the section making it suitable for assembly with mitred joints. It is available in any RAL colour and the heavier wall allows the section to be bent to much smaller diameters than the welded equivalent.