A suitable power-driven tensile-strength testing machine (with a constant rate of traverse of the pulling jaw of 500 ± 30 mm per min) calibrated in accordance with SABS Method 118, Choose the working range on the machine that will give the greatest accuracy. Use jaws each having one face of size 25 mm x 25 mm and the other face at least 25 mm x 50 mm (the longer dimension being in each case at right angles to the direction of the applied load), of a type that will not cut the specimen, and with one or both jaws free to swivel.