uPVC 400mm Replacement Fascia Board (18mm Square Edge) 5m - Black Ash Dimensions Length: 5m. Width: 400mm. Thickness: 18mm. Material: uPVC. Guarantee: 10 years. Description The magnum square leg fascia system is a clean, modern style which includes the 18mm thick fascia board and a full range of accessories to ensure a neat and professional installation. The magnum square leg fascia system comes in a wide range of solid colours, woodgrain finishes and fascia widths.