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Rizzato ones will have the (nominal) frame size in inches marked in two places on the underside of the bottom bracket shell -



As mentioned by T-Mar, serials are marked on the drive side of the seat tube a few cms below the seat lug. The first two characters are numerals which give the year of manufacture -



If the cycle has a cottered steel chainset you may find an Atala marking on the centre section of the bottom bracket spindle.

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