This element comprises an elongated, annular body (10) being shaped as a band being made of a resilient and tough material and defining two elongated lengths (12) facing each other, said lengths being connected to each other through curved end links (13). First and second fastening members (31, 32) connect said elongated lengths (12) to respective first and second portions being likely to effect relative motions. Said second member (32) advantageously connects the body (10) to said second portion through a second body (20) having an analogous configuration and through a third fastening member (33). When facing the motion three-dimensional components the bodies (10, 20) operate by means of longitudinal shifting motions of the elongated lengths (12, 22) in mutually perpendicular directions (D1, D3) and by means of motions of the elongated lengths (12, 22) in another direction (D2) being perpendicular to the previous ones, these latter motions bringing said lengths closer together or farther apart from each other.
