hi,
i would like to know how the sizes of an old MTB bianchi thomisus really work (and in general in that range of bianchi´s 90´s MTB: theridion, ragno, etc.)
i mean of course in what sizes they were originally offered, but also what do these seizes mean (do e.g. a size 50 on these old MTBs actually mean 50cm center to center? and would this correspond to the standard road bike size 50?) i would very mach apreciate some orientation with that...

thanks in advance!

here´s a photo from the internet: