Most Cinelli bars I've seen have the size stamped on it. 66-42 would be a model 66 (Campione del Mondo) in width 42 cm, however it's measured. That may not be true of your bars, which appear to have an “old logo.“ Try VeloBase.com. Maybe your caliper's off, or maybe they were made for another market than the usual 26.4 center section.