US Patent 8695644 Tubular duct member

A tubular duct member comprises a plurality of sheet metal panels 10, 12 joined along adjacent longitudinal edges by cooperating folded sheet metal catches 14, 16, the catches being pushed together such that respective detent surfaces 28, 30 on each catch engage behind one another to retain the edges of the sheets together. One of the catches 14 includes a body 36 of resilient material compressed between the catches and biasing the catches apart to maintain the detent surfaces 28, 30 bearing against one another.