Replacement gearbox for ICS CXP-MARS series AEGs. This high quality Version 2 split gearbox comes fully built and ready to drop-in your favorite AEG. An Inline Trigger MOSFET, Quick-Change Spring System, and POM Reinforced Piston with Steel Teeth are just a few of the innovative ideas ICS has integrated into this next level gearbox. This gearbox offers simulated blowback to increase authenticity and overall fun when using this inside your AEG. The Selector Switch located on your rifle will release spring tension to maintain spring strength and prevent wear and tear. Upgrade your AEG with this gearbox option from ICS.