The VFC Avalon ECS M4 Complete Gearbox.  M4 Avalon AEG style, fits in all the VR16 Avalon guns by Elite Force.  A fully built and ready to drop-in gearbox with all its parts ready to go.  Fits airsoft M4 AEGs (VFC) and may fit other models.  Comes with what is pictured.  A very high quality Version 2 (V2) gearbox made by VFC ready to go.  Other gun compatibility info TBD.