The newest generation of the CRBN Upper is here!  CRBN Uppers are a sleek way to turn any build into a lightweight beast, made with genuine carbon fiber for strength and durability. The Gen 3 has been upgraded to include dual hopup windows, fiber-optic back sights, perfect fitment, and updated threads. Plus, a reduced price to increase accessibility! All uppers are cross-compatible, so you can swap your tubes and parts between any of your CRBN uppers!  This Gen 3 CRBN Upper Includes: Gen. 3 CRBN Upper: CNC milled Carbon Fiber and ABS Polymer Genuine Carbon Fiber tube Fiber optic front and rear sights for fast target acquisition Dual hopup windows for on-the-fly adjustments Perfected drop-in fitment on a G&G lower with a Maxx hopup Included Fiber Optics Rods (Green and Red) Available in Glossy Black, Matte Black, Red, Blue, Purple, Silver, and Gold tube colors Compatible with: Polarstar Fusion Engine (Drop-In) F2, Jack, Inferno, N7, etc. (Requires CRBN Gearbox) G&G polymer lower receivers (Link->https://airtaccustoms.myshopify.com/products/g-g-cm16-sr-style-polymer-lower)  (SSG1, ARP9).  Monk Customs and EMG F1 lowers (with modifications) CRBN Uppers are EXCLUSIVELY compatible with  (Link->https://airtaccustoms.myshopify.com/collections/maxx) (ATPRO, M4P, M4A) AirTac Customs  CRBN Gearbox (Link->https://airtaccustoms.myshopify.com/products/airtac-customs-crbn-gearbox)