Enhanced Recoil Spring is made of high strength spring steel. Its short length design with 2 different tensioned coil zone (140% / 120%) can enhance the efficiency of recoil cycling. Also, it can improve the recoil control and make easier handling on blowback cycling. Compatible with Tokyo Marui M&P9 and Glock Series. Highlighted features Made from High Strength Spring Steel Hard Coating Prevents Corrosion Shorten length with harder coil Improve cycling efficiency Cycling enhancement through 2 different tensioned zones (140% / 120%) *PS: Please note: installing parts / assemble /fitting airsoft gun will need intermediate knowledge; for expert or airsoft gunsmith. Please refer to your airsoft gunsmith for proper installation/fitting. Fitting may be needed as the condition of each airsoft gun might be different. Regular maintenance is needed for all airsoft guns in order to keep it in good working condition and reduce wear out issue on parts.