Shimano Deore spec level Di2 derailleur, part of their amazing wireless 12-speed mountain bike drivetrain range.

SPECIFICATION - 

• Precise and clean wireless shifting with Integrated on-board removable battery (BT-DN320 sold separately)
• The integrated removable on-board battery is protected within the linkage
• Crash recovery function, absorbs impacts and returns to its original position
• Connectivity BLE, ANT private
• Shadow ES features a super low profile skid plate design and optimized slant angle for optimal clearance
• Shadow ES uses a dual spring chain stabilising switch that when on will reduce chain bounce in rough terrain maintaining more stable drive and shifting
• The Shadow ES system is also zero maintenance and has no degradation of performance
• Unique structure using two springs has a tighter chain wrap that improves shifting and security with increased spring force by 70%, allowing the chain to mesh firmly with the sprocket
• With the tighter chain wrap skipping is prevented even as the cogs wear
• 13T solid pulleys and decreased derailleur tension prevent high chain tension in low gears
• Dependable steel pulley cages
• Cold forged wide alloy links and pivot body
• Fluorine-coated link pin bushings
• Specifically designed to work with 12-speed drivetrains
• 10-51 tooth compatible SGS cage