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device and procedure for reduction of risk for leckage from a first side to the other of the layer materials and tools for the implementation of the device, and
device and procedure for reduction of risk for leckage from a first side to the other of the layer materials and tools for the implementation of the device, and
A hole (4) is formed in the material sheet (1) to take a screw bolt (3). It has its edge part bent towards the first side to constitute a raised formation (9) around it.
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