UDH (Universal Derailleur Hanger)
UDH (Universal Derailleur Hanger) is SRAM's standardized derailleur hanger. The hanger is the «fuse» between frame and rear derailleur: it breaks to save the frame in a crash. There used to be hundreds of different hangers; UDH unifies that interface into one, mounted concentric to the thru-axle (M12×1.0 thread). A UDH frame is also the requirement to fit SRAM Transmission (T-Type) direct-mount derailleurs, with no hanger. Note: the frame must be designed for UDH from the factory; it isn't a universal adapter.
It's the part that ended the «which hanger does my frame take?» nightmare. And, along the way, it opened the door to SRAM's most modern drivetrain.
What it is and what it solved
Traditional hangers differ on every frame, a spares nightmare. UDH defines one geometry any brand can adopt. It mounts around the thru-axle and is designed to rotate backward on impact, dissipating energy. Its big bonus: UDH frames can take SRAM's T-Type derailleur, which bolts straight to the frame (Full Mount), replacing the hanger.
Key data
What it fits
A frame designed for UDH + an M12×1.0 thru-axle. On a UDH hanger you can mount any traditional derailleur (Shimano, SRAM, Campagnolo) with its standard thread. To fit a SRAM T-Type/Transmission derailleur, the frame must be UDH (the derailleur replaces the hanger). It doesn't work on quick-release frames or old frame-specific hangers.
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Frequently asked questions
Does UDH fit any bike?
No. The frame must be built specifically for UDH. If your frame isn't UDH, you can't convert it.
Can I mount a Shimano derailleur on a UDH hanger?
Yes. The UDH carries the standard derailleur thread, so it accepts traditional Shimano, SRAM or Campagnolo.
Do I need UDH for SRAM Transmission (T-Type)?
Yes, mandatory. The T-Type derailleur is Full Mount: it bolts to the frame replacing the UDH hanger. Without a UDH frame it's impossible.