Do you want to add another bottle cage to your bike but don't have the mounting holes? Just use these clips, this one was originally designed for the seat tube of my bike, with a diameter of about 34,5mm. It nicely snaps on and is tightened on by heavy duty zip ties. On the inside you can put the appropriate nut, which usually comes with the bottle cage. Or just get yourself an M5 screw and nut from the hardware store and print yourself the Prusa bottle cage featured in these pictures, ideally from ASA. You can find that here:
https://www.prusaprinters.org/prints/5003-asa-bottle-cage
Should be fine to lay it flat, it does have small a 60° overhang that way, but an MK3S can deal with that.
The author hasn't provided the model origin yet.