PEEK Expandable Interference Screws The raw material of the screw part of the expandable interference screws, which is designed to function like a dowelled system with a superior and unique design, is PEEK OPTIMA®. Internal Expansion pin is made of ASTM-F136 titanium alloy. Compared to standard interference screws, this implant provides the best and most superior contribution to the bone-tendon attachment by ensuring perfect surface contact as long as the length of the screw. 1,3mm-large expansion created by the internal expansion pin of the screw ensures that all exterior surface of the screw –as long as the length of the screw- puts a pressure on the bone tunnel surfaces together with the tendon and this creates excellent attachment.