This Valken AEG main spring replacement is suitable for any version of Airsoft AEG gearboxes. Its made of high-quality steel that doesnt stain and is extremely durable. The wire tension is accurately measured to ensure the best possible performance. This AEG spring provides approx. 260-320 FPS, a great indicator for the value. Naturally, the actual FPS may differ from the estimate depending on the alignment, power output, installation, inner barrel, cylinder, and more factors. The spring is made to reduce the stress and tear of your gearbox.