The ASTM E23 Charpy testing standard uses a 2-2.5mm radius striker whereas BS EN 148-1 can use either a 2mm or 8mm striker. Consequently, for materials with a high Charpy energy (above approx. 100J), more energy will be absorbed by the 8mm striker than by the 2mm striker equivalent and tests carried out using the 8mm striker will report higher impact energy. Even if ASTM E23 and BS EN ISO Charpy tests both use the same test specimen and striker radius, at TWI the specimens are tested on different machines which have been calibrated to different agency reference standards.