The hinges form the technological heart of the sea defence system. They constrain the gates to the housing structures, allow them to move and connect the gates to the operating plant. The steel gates consist of a male element (3 metres (9.8 ft) high and weighing 10 tonnes (9.8 long tons; 11 short tons)) connected to the gate, a female element (1.5 metres (4 ft 11 in) high and weighing 25 tonnes (25 long tons; 28 short tons)) fastened to the housing structure and an attachment assembly to connect the male and female elements. A total of 156 hinges (two for each gate) will be fabricated, together with a number of reserve elements. Fabrication is currently underway.