Mod for swapping fuel types

[Kerbonautical]

I had this mod at one point and I can't remember for the life of me which one it was that allowed it. It was a mod that let me swap between different fuels that parts could carry. Considering Nerva engines now rely purely on oxidizer this seems like as good a time as any to have such a mod. Can anyone remember which mod it is? I keep thinking Interstellar for some reason but I have no idea why since that's a completely different mod.

[panzer1b]

look up modular fuel tanks

its one mod that simplifies the job of having to manually go into .craft files and messing with fuel loadouts. Honestly id make this stock, its not a cheat or something that makes no realistic sense that we are given the option to pick fuel ratio or even fill a LFO tank with pure O or pure LF...

[kerbiloid]

Also FreeThinker's Interstellar Fuel Switch

http://forum.kerbalspaceprogram.com/threads/117932-1-0-2-Interstellar-Fuel-Switch-0-7-%28released-5-5-2015%29

or using Firespitter plugin.