A few early adopters went rouge on their own for axle threads. See Norco. Also there were some spec changes at some point in the early life of UDH that wasn't well communicated so there are some "UDH" bikes out there that can't actually fit Transmission. See Cotic.
You can also have a dropout that's Transmission compatible that doesn't meet the UDH hangers specs, a number of small steel framebuilders are going this way. The UDH hanger has some features to limit it's rotation that are not needed for Transmission and by ignoring these the dropouts can be slimmed down.
June 23, 2023, 11:13 a.m. - earle.b
A few early adopters went rouge on their own for axle threads. See Norco. Also there were some spec changes at some point in the early life of UDH that wasn't well communicated so there are some "UDH" bikes out there that can't actually fit Transmission. See Cotic. You can also have a dropout that's Transmission compatible that doesn't meet the UDH hangers specs, a number of small steel framebuilders are going this way. The UDH hanger has some features to limit it's rotation that are not needed for Transmission and by ignoring these the dropouts can be slimmed down.