I replaced a pair with aluminum pulleys on one of the bikes I used to own, and then wondered why it seemed to shift better than my other Nuovo Record bikes. It must have been the pulleys.
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1971 Paramount P-13 Chrome
1973 Paramount P-15 Opaque Blue
1974 Raleigh Professional Blue Mink
1991 Waterford Paramount
Holland Titanium Dura Ace Group
Holland Titanium Ultegra Triple Group