Guides / Process
Machining Derailleur Hangers, Including UDH
September 16, 2026
A derailleur hanger is the cheapest structural part on a bike and it is deliberately the weakest. It exists so that when the derailleur takes a hit, something replaceable gives way instead of the frame’s dropout. Designing and machining one means designing a part to fail correctly.
Design for yielding, not for strength
This is the part where the usual instinct is wrong. You do not want the strongest possible hanger.
Material. 6061-T6 is the standard and the right answer. It yields, bends and absorbs energy. 7075-T6 is stronger but less ductile, and a hanger that snaps clean lets the derailleur swing into the wheel, which turns a bent hanger into a destroyed wheel and possibly a crash.
Thickness. The section at the bend zone is the design. Too thick and the hanger survives while the dropout deforms, which is a frame repair instead of a five minute part swap. Too thin and hangers bend in normal riding and the bike never indexes properly.
No stress concentrations in the wrong place. The hanger should bend across a broad section, not tear from a sharp corner or a bolt hole.
Where the tolerances are
Despite being a simple looking plate, a hanger has fits that matter:
- Derailleur mounting thread. M10 by 1.0 on most modern hangers, and the thread axis has to be right. If it is out, the derailleur hangs at an angle and no amount of B screw adjustment fixes the indexing.
- Mounting face flatness and parallelism. The hanger sits between the dropout and the axle. Faces that are not parallel put a bend into the assembly as soon as the axle is tightened.
- Location features. Dowel holes, tabs or a machined step that locates the hanger in the dropout. These are what keep the derailleur position repeatable between hangers.
- Overall geometry. The position of the derailleur mount relative to the axle center sets the chain gap. This is the dimension that makes a hanger frame specific.
General tolerance of plus or minus 0.1 mm with the thread position, the locating features and the mounting face parallelism called out tighter is normally the right structure.
What UDH changed
SRAM released the Universal Derailleur Hanger in 2019 and licensed the geometry to frame makers for free. The idea is exactly what it sounds like: one hanger shape that fits every frame designed around it.
Consequences for anyone making hangers:
- One geometry instead of hundreds. For the frames that use it, the endless catalog of frame specific shapes collapses into one part. That changes the economics completely, because now you are making one part at volume rather than fifty at low volume.
- It is a defined standard. The interface, the thread, the axle path and the rotation behavior are specified. Do not improvise any of it.
- It mounts through the thru axle and is designed to rotate rearwards on impact rather than bend, which is a different failure mode from a classic hanger and a different design intent.
- Full Mount derailleurs bolt to the UDH interface directly, which means the interface on the frame is now carrying a derailleur mount, not just a hanger.
Many brands including BMC, Canyon, Cervelo, Specialized and Trek use UDH on at least part of their ranges, so a machined hanger business that ignores it is aiming at a shrinking segment.
The aftermarket reality
Frame specific hangers are a high mix, low volume business: hundreds of geometries, small batches, long tail. The machining is not difficult. The hard parts are:
- Getting accurate geometry for each frame, ideally from the frame maker rather than by measuring a bent sample
- Holding a catalog of programs and fixtures
- Keeping small batches economical, which comes back to batching parts through one anodizing run
A shop that can set up a family of similar parts on one fixture and change only the profile program handles this well. A shop treating each hanger as a fresh job does not.
On the RFQ
Say the material and temper, whether it is a UDH or a frame specific part, the thread and its position tolerance, the mounting face parallelism, the locating features and the finish. Attach a STEP file and, for frame specific work, say where the geometry came from.
Send it on the RFQ form and shops that already run hanger families will be quick to answer.
Frequently asked questions
Should a hanger be made in 7075?
Usually not. A hanger is a sacrificial part designed to yield before the frame or the derailleur does. 6061-T6 bends and absorbs energy. 7075 is stronger and more brittle, and a hanger that snaps instead of bending can let the derailleur into the spokes.
What is UDH?
SRAM's Universal Derailleur Hanger, introduced in 2019 and licensed free to frame makers. One hanger geometry across every frame that adopts it, mounted through the thru axle, designed to rotate backwards on impact rather than break. Many major brands now use it.
Can I machine replacement hangers for older frames?
Yes, and it is a large aftermarket. The difficulty is not machining, it is geometry: there are hundreds of frame specific hanger shapes and each needs accurate dimensions taken from a good sample or from the frame maker.
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