As [MENTION=425264]tyrion[/MENTION] mentioned, unless the cages are the Arundel flip-flop, you're going to need one of each-- a lefthand and a righthand. I assume the cages to be the Bontrager side load, so you would want one of each.

If your frame is tiny and only fits one cage... what hand do you usually grab the bottle with? I'm right handed so I use the right.