You're right, a treble is in F (which means that if you cover up all the holes, you play an F).
They alternate between C and F, here is a list showing the note you get if you cover all the holes:
Piccolino - F two and a bit above middle C (but you can't actually buy these - someone just made one as an experiment!)
Garklein - C two octaves above middle C (would be written as middle C).
Sopranino - F one and a bit octaves above middle C (written F above middle C).
Descant (aka soprano) - C one octave above middle C (written as middle C).
Treble (aka alto) - F above middle C.
Tenor - middle C.
Bass - F below middle C, written one octave lower (i.e. the F below the bottom line on the bass clef).
Great Bass - C below middle C (written one ocatve lower).
Contra Bass - F one and a bit below middle C (written at sounding pitch).
Sub contra bass - C two below middle C (written at pitch).
Sub-sub-contra-bass - F below that (written one octave higher). With a forklift truck for carrying
Here is a link that shows you the ranges.
Here is a picture of the Hampshire Recorder Sinfonia modelling garklein to contra-bass to show the sizes.