Although there are several clamp and hook/stand designs, I needed one that can be tilted along two axes (front-back and left-right), since my mounting bar was not level (see third photo). Hence this design, which is also fully customizable (all dimensions in mm).
Originally started as an iPad stand for a stationary bike (example shown, using a pair of clamps), but soon became a generic, customizable design (all clamp and hook/stand parameters can be adjusted). Looking forward to see how people use it!
All dimensions are in mm. Measure and customize according to your needs. Fastener parameters can be adjusted in "advanced settings" tab; defaults are for M3 socket cap screws.
Please note that parameter constraints are not enforced, only listed in parameter descriptions. You need to be particularly careful when changing thickness (lest screws do not have a thick enough surface to rest upon).
Mine are printed in ABS, so clamps flex nicely when tightening (I haven't tried PLA yet). If you dramatically enlarge clamp gap (relative to radius) or print in different materials, you may also need to tweak the thickness CAD parameter and/or the shells and infill slicing parameters for the clamp piece.
I sprayed a light coat of Plasti-dip on the flat outer surface of the clamp, to increase holding friction. That doesn't seem necessary in retrospect, but perhaps an option to keep in mind.