UDH is a standardized rear derailleur hanger introduced by SRAM in 2019. It reduces the need to find a hanger made specifically for each frame. A UDH supports a traditionally mounted derailleur, and the interface appears on mountain, road and gravel bikes.
The hanger is designed to rotate backwards under impact. It is not exclusive to SRAM derailleurs: on a compatible frame, UDH also works with traditional mountain bike drivetrains from other manufacturers.
Full Mount describes a different attachment: the derailleur connects directly to the frame’s compatible interface, replacing the UDH hanger. A UDH hanger and a Full Mount derailleur are therefore different components.
Before buying, identify the frame model and year and check the manufacturer’s compatibility information. “Universal” does not mean it fits every frame. When changing drivetrains, check chain, cassette and derailleur compatibility separately as well.