The ULTIMATE® springs are named M90 M100, M110 etc. according to their expected tension in meters per second - measured when using a 0.20gr BB and a 300mm long barrel. In turn, a M110 spring would give 110 m/s. To convert to feet per second (fps) simply multiply by 3,28, e.g.: ref. 16671 - M120 - 120ms/394fps.