Description: The SHS M90, M100, M110, M120 and M130 Upgrade Springs are an excellent alternative to the other springs currently available on the market. It can be used in almost any AEG gearbox and is made of steel piano wire for enhanced durability, reliability and longevity. Upgrading your gearbox with this spring will increase FPS from 430-600, results may vary. It is suggested to check your gearbox to make sure the supporting parts can handle the strength of this spring.Specifications: Manufacturer: SHS Model: Upgrade Piano Wire AEG Spring Color: Silver Material: Metal Features:Metal ConstructionCompatible in any AEG airsoft gun gearboxesPlease Note: Professional installation is recommended. Improper use or installation of upgrade parts are 99% of the time the cause of failures of these items.Please thoroughly inspect any parts for defects before attempting installation. Due to the high possibility of damage from improper installation, we will not warranty parts after attempting installation.Package contents included by the manufacturer may varyPlease check the fps table below to make sure which spring is fit your need.M90 : 310-330fpsM100: 330-350fpsM110: 350- 380fpsM120: 380-410fpsM130: 410-430fps