Dating campagnolo chainrings
They used a square taper fitting on the spindle instead of the cotters used by most steel cranks at the time.
As their name implied, these cranks were strong and light. The chainring attached to a small flange on the right crankarm, as was common among cranks at the time.
The next modern aluminum crank was offered by René Herse in 1938 (above; 1950s tandem version shown).
Herse mounted his chainrings to a larger spider instead of a flange.
The parallelogram which revolutionized gear changing. Above (4 fotos): in 1987 Cinelli offered a special edition, called the Golden Black, featuring extensively re-worked Super Record components.
Modern cranks are an interesting story of standards that evolved until nobody remembers why they were adopted in the first place.
(Source: Frank Berto - "The Dancing Chain") See photos below One of the most important years for Campagnolo.