"The aerodynamic cone shape reduces frontal air pressure caused by the blunt end of a water bottle and reduces drag (independently tested to save 4 watts). Marginal gains, but it all counts over 180km!
Fits all standard 63-65mm cages.
Turns your cheap water bottle into a sleek and slippery Torpedo. A smart, low cost addition to optimise your Tri bike cockpit." - Fast TT
 
Aero cone to add to Fast TT BTA (between the arms) system, to reduce aero drag around a standard bottle. Cone only, bottle cage and mount sold separately