Abstract: A device comprising a frame composed of lengths of tubing and coupling pieces interconnecting the same, coupling piece and coupling piece parts for the same, each coupling piece having a cubical body provided on each outer face with a recess with undercut engaging rims for receiving a base part of an arm connected with a tubing and having complementary engaging rims in a manner such that the arm is fixed in place at least in the direction transverse of the outer face. The edge of the body is equal to the thickness of the tubings, the body consists of two identical parts having a square head face, each part having complementary connecting means for joining a body part by a base face to the base face of the other body part in a direction transverse of the head face, while each side face has a recess which is accessible only from the base face for the base part of the arm and which forms, together with a corresponding recess in the other body part, the recess for receiving the base part of an arm.