Abstract: The invention relates to the fabrication of panels, trays and other assemblies from fibreboard or other sheet material by folding-back edge portions of the sheet to provide marginal portions of increased thickness and substantially uniform width of which the inner edges define retaining abutments, each marginal portion being located in a channel of respective channel-shaped edging strips each having a lip or rib which engages over and with the retaining abutment of the marginal portion to resist separation of the strip from the edge of the sheet in the direction perpendicular to said edge. The edging strips are assembled to an edge by forcing the channel over the marginal portion. Adjacent edging strips engage to resist sliding movement.