DT240 End Cap Length: 15.9 mm
Roval CL50/Roval hub with DT350 internal end cap length: 17.1 mm
Question out to DT Swiss around why and specifics. My guess is it's a MTB end cap. Oh well, i'm setup with the correct end cap on the way.
Pics:
Correct length from DT350
Shorty from DT240
