An essential component reimagined by AirTac Customs - the ALU CRBN Gearbox is a functional and lightweight gearbox for M4 rifle builds, now in CNC Aluminum. Our CRBN Gearbox enables you to use a CRBN Upper with ANY M4 HPA engine system! It's now possible to use drop-in engines such as the P* F2, Jack, Gate Pulsar, and Inferno in CRBN builds! Sporting an innovative 3 piece design and available in 10 classic colors. This AirTac Customs ALU CRBN Gearbox includes: AirTac Customs ALU CRBN Gearbox: - Skeletonized Lightweight Design - CNC 6061 Aluminum construction - 10 Brand New anodized Colors! - Removable trigger door for easy trigger tuning and swaps - Left/Right alignment screws for full alignment control - Up/Down alignment screws for maximum clamping force - Allows compatibility of a CRBN Upper with any drop-in HPA engine - Does not include selector plate Compatible with: - [CRBN] G&G-style V2 Lowers (SSG1, ARP9, SSG556, etc) - Any other V2 lower, upper, and grip. - Any standard M4 HPA engine