the invention relates to a double assembly system that can be used for pivoting , rotating or folding operations . the invention is suitable for use in the production of furniture or other construction elements and structures , for the purposes of folding and unfolding , opening and closing , and , depending on the spatial orientation thereof , for securing a part in its use position . the invention can be used to join generally planar parts . the invention is formed by a group of elements which are interlocked with other elements and which , when joined , allow a rotational movement through a specific , pre - defined angle .