What's the numbering system for spaghetti and does it matter? When I lived in Italy some years ago I remember an Italian friend explaining the numbering system for spaghetti (perhaps also other long pasta). How spaghetti was sold in Italy with a number indicating its fineness. 

She told me that different kinds of recipes called for specific numbered spaghetti, if you wanted to be precise.

Can anyone else explain the numbering system for spaghetti better than my vague recollection? Do people in Italy really worry about matching the right numbered spaghetti with a given dish, and has anyone outside Italy encountered a recipe calling for a specific number spaghetti?
Ok, here is the straight dope, directly from De Cecco customer service:


  With reference to your question we would like to inform you that the numbers you mention do not have a logical criteria but are just code numbers which we give our products each time we make a new shape.