Summary

This is my attempt to design a holder for Kryptonite u-lock, as I happen to have one without a frame mount and, it's quite a heavy thing to carry in ones backpack.

Designed for 28.5mm frame tubes. But editing the clamping part, can make it easy to mount to other types of frames.
Requires 4 M6 bolts with hex head of 40mm length

UPDATE:

So after the PETG only version failed, I added some fillets on the model, to get rid of stress concentration points. And also, I've printed it as TPU + PETG composite. So first 4.4mm are made of TPU, that allows for better mount to the frame, then we have PETG up to 9.2 and more TPU from 9.2 to 26. That second TPU part works as vibration damper, and so far it works great. It is also important to have 100% infill two layers before and two layers after change from TPU to PETG and back, to achieve maximum adhesion.
I'm riding an all rigid bike, and I've got plenty of potholes cracks and cobblestone on the roads here, so I do get a lot of vibrations.

Also, added tubular fasteners to prevent too much deformation that can cause cracking.
And the last version I've printed on a 0.6 nozzle.