My Trelock U-Lock wasn't fitting properly to my bike. Thus, I designed my own mount, that attaches to the seat post (27.1mm in diameter).
Print the bracket two times and the holder once. I've used 4 short M5 screws to screw the bracket and holder together. M5 threads (with enough clearance for a 3D-printer) are designed right into the lock holder.
I've attached the FreeCAD project and also the Trelock mount itself to use it for remixes.
The author marked this model as their own original creation.