[Zope] Private Products

Hello all: I'm newby with zope... I want create a Product for example named "Factory" that includes another Products like Machines, Tasks, etc... But I don't want that these Products (Machines, Tasks, etc) to be "addables" in the Add List, only the Factory... How I can do this? It's posible? For now, I have created a Product Factory and a normal python class named Machines, but I don't want this... Thanks...