EN 74-2 specifies: - materials; - design requirements; - specified values for resistances and stiffnesses which a coupler has to achieve under test;  test procedures and assessment; for the following special couplers:  screw or wedge half couplers, sleeve couplers with shear studs, right angle reduction couplers and swivel reduction couplers. It gives recommendations for on-going production control. These couplers are for use principally in temporary works. Each coupler is able to be fixed to at least one side to one 48,3 mm diameter steel or aluminium tube. For the other side of reduction couplers, this standard specifies requirements for the diameter and wall thickness of tubes. For testing, screw couplers are tightened with a torque of 50 Nm and wedge couplers are tightened with a 500 g hammer until the jarring blow. Other special half couplers such as half couplers attached by riveting, used mainly for members of prefabricated scaffolds, are outside the scope of this European Standard. NOTE Information on design using special couplers is given in Annex B.