Airsoft Shooting Gear E&C 8mm Complete QD Transform M-Series AEG V2 Gearbox Version 2 Rear Line Wiring 2pcs 8mm ball bearings, 4pcs metal bushings. Quick release spring and spring guide for easy power adjustment / spring replacement. Replaces all major brand M4 standard gearbox. Weight - Approx 507g Go to the middle left of the page to see the full Product Description.