The three cornered construction can be expanded by the addition of extra components. It is formed of units (10) joined by a rotating fixing mechanism (9). The units are triangular with equal angles of 60 degrees and have three mortices (2, 3, 4) for the positioning (6) of the fixing mechanism (9) and to allow a tool to be positioned. There is a drilled hole (1) for the insertion of a pin (4). The units are fixed together by a ductile spiral spring (8) which is attached to a circular component (7).The whole unit can be made watertight by the injection of a product
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