CNC aluminium device which fill the space around HopUp chamber. Holds weak front part of the gearbox and prevents agints breaking. Even more! Keeps wracked gearbox in the possition and allows to continue with playing. Improoved design allows to use on the most common M4 AEG brands, such as AimTop,Matrix, Classic Army, Dboys, A&K, SRC, P&J, , G&P. Not suitable for two piece hopup chambers.