This is designed to snap a compact bicycle pump to the seat tube of a bicycle. (Normally these pumps would be mounted on a water bottle boss, but my frame's suspension interferes.)
It's designed for a 31.6mm diameter seat tube and a 27mm diameter pump. (The part's diameters are 5% less so that it snaps together tightly.) If you want other dimensions, let me know and I can change it for you. (Thanks OpenScad!) Many bikes use a narrower 27.2mm tube.
The height is 40mm, and there's a 25mm tall hole in the center for velcro straps to pass through.
I haven't tried it out yet, so I can't speak to how well the snapping works.