Kryptonite U-locks often come with a two-part bracket designed to be strapped to a tube on the bike's frame. On a folding bike like mine, there isn't a good place to put the strap where it won't be in the way or slip down constantly, so this adapter allows the top part of the bracket to be bolted to a standard bottle cage mount (one with 64mm between the bolt centres).

To use it, undo the central bolt of the bracket all the way, leaving you with the two plastic parts, the bolt, and a square plate that works as the nut. Then put the top part of the bracket onto the adapter at the desired angle, drop the nut into the hole on the underside, then tighten the bolt through the hole on the top. (The screw hole is intentionally a little small, so that the bolt's screw will dig into the sides. If you're printing with something harder than PLA or ABS, you may want to widen the hole by modifying the #bolt_diameter variable in the Onshape model before printing.)

Onshape model

I am not affiliated with Kryptonite.

Change log

v2:

• Thickens the plastic underneath the central stud, since this broke for me on a recent ride. (Why I only made it a couple of mm thick in v1, goodness only knows…)
• Offsets the lock mount by 1.5mm relative to the bottle cage mount, making it fit slightly better on my bike.