Made to fit for a DM556 stepper driver but others might work too
See drawing with measurements for detail.
.step available too if you want to modify it.
If you ae looking for a DM860 holder, mybe have a try with this one:
https://www.printables.com/model/1321810-din-rail-stepper-driver-holder
The author remixed this model.
Cut to lengt and added some extrusions