This is a custom designed camera side handle. I modelled this in FreeCAD (file available for customizing). The counterbore holes are 7mm diameter with 11mm bore (5mm surface thickness at the face). The holes are each 18mm center-to-center.

The "material saver" core-outs also serve as slight ergonomic spots so you can rest your fingers in there, getting a little extra grip.

I attach this to my custom modeled 70D cage, but with the 18mm hole distance you should be able to attach this to many cages.

I used PETG for the strength, heat resistance, and impact resistance.