The smallest item on the order can determine the tightness of a large roof area. A screw on its own is not yet a complete fixing. Fibre cement sheets require the correct shank, a pressure and sealing component, and a hole made in accordance with the system. Asbestos-free fibre cement should therefore be priced together with the accessories. Replacing them with a random set makes it difficult to predict how the connection will behave under wind and during temperature changes. The shank transfers forces to the substructure. The pressure component distributes the load over the intended area, and the seal limits water ingress. The shape of the head and the way the tool is guided are also important. Damage to one component can weaken the performance of the entire set.