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Hello Slick4d4d,
have had this chainwheel pattern come through on at least three or four machines over the years.
have also seen it worn by two-wheelers encountered "in the field."
in each case it was either unmarked or marked only with the name of the cycle.
Bianchi, for example, employed it on the planetary three-speed models of the 1950's and early 1960's.
at the era of the subject bicycle the Italian manufacturers of cottered steel chainsets were these -
Agrati
FB (Fratelli Brivio)
Giostra (Magistroni & OMG)
Gnutti
Way-Assauto (WA)
of these five producers suspect the best candidates to be Agrati and Giostra; with Way-Assauto as a somewhat less likely possibility.
there be a strong likelihood that the maker of the machine's chainset is is also the manufacturer of its bottom bracket fittings.
possible that the outer faces of the bottom bracket cups may carry a marking...
a better chance is that the centre section of the bottom bracket spindle will carry a marking.
if Agrati, it may carry the Agrati name.
if Giostra, it may carry an OMG marking in an oval recess.
the letters in this case do not stand for "Oh My God!"
but rather Officine Mecchaniche Giostra.
another possibility for a marking is a single letter such as a captial letter C.
lastly, a two digit number such as 57, this is an indication of the distance between the spindle's bearing shoulders as measured in mm.
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cycle as a whole -
the overwhelming majority of house branded chainstore bicycles contract manufactured in Italy for U.S. companies from the 1950's through the early 1970's were produced by the firm Chiorda - Italy's largest producer in terms of unit volume at the time.
do not especially see any Chiorda traits on your machine.
this is because of the cantilever frame design which in not very common in Italy - usually seen only on some juvenile models.
unable to make any specific guesses as to maker.
another large Italian producer of the era who made a good number of contract produced cyles was Cesare Rizzato; maker of Atala, Atlantica, Corso, Lygie, Maino, Radius & other marques.
this firm was a "full line" manufacturer who offered juvenile, folder, planetary three-speed, town (condorino) and "racing" bicycles.
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fittings other than chainset -
the bicycle's fork crown & its headset are from Agrati.
other bits which appear they may be Agrati items include front hub, fork ends, dropouts, bottom bracket shell, pedals and plate style bridges.
chainguard and mudguards may be products of Mazzucchelli.
seat binder collar and bolt appear they may be from Way-Assauto.
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presently thinking early-to-mid 1960's for a date.
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photo tip -
six images of cycle provided, all of which are down-angle ones. down-angle is preferable in a few cases. in general, the eye receives more information about the bicycle when pictures are taken directly straight on - no up-angle nor down-angle.
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