Designed for Triathlon specific purpose but can be used as a cage mount for any bike with 27.2 seat post. Snaps on to seat post then zip ties in place (found that a wrap of electrical tape under it helps it to stay put and not rotate as easy).
Bottle cages mount with #10 x 1/2" screws and nuts, there are recesses to hold the nut from turning so only a screw driver is needed.
The area between the water bottles is meant for a road tube (I like to add tube infiltrator and quick sticks into a zip lock), I have a Velcro strap to make sure it doesn't bail on me if i hit a bump. The out side openings have room for (2) 16g co2 cartridges that snap into place.
Also take a look at the Number flag snaps to post
I used a thicker wall and less infill give good strength but nice and light, this was printed in PLA Which works really nice (note warming up outside smooths off the exterior nicely I used propane torch and waved it back and forth after pictures were taken) watch supports in Zip tie holes they're a bear to get out had to use exacto knife.