double Slot Backup & Expansion ( Select Models) Designed for D850 and for GFX50R cameras, ensuring professional data security and management flexibility Video for high bitrate 4K video, these slots require UHS Speed Class 3 ( U3) or cards to maintain stable data writing, interruptions during critical footage capturing double Slot Design for D850 features + UHS II slots, while Z6II offering CFe / + UHS II slots, universally compatibility Wide Compatibility & Fast Speed supporting fast speed bus standards for faster read / write speeds, enhancing continuous video for D850, Z6II, and other models Verified Reliability & Brand Compatibility Officially tested with leading card brands, this metal slot meets strict standards for long term use in professional photography environments