Sistema Contour Ring (Charm Version, 9mm, DA+PA)Sistema Contour Ring (Charm Version, 9mm, DA+PA) from Parts of four. Sistema series The Sistema series is first family within Parts of Four. As a mode of creation it expresses the core principle of P 4 which is modularity. The "body" and "insert" are separate parts joined together with pins. This leaves endless possibilities for iteration of material and form combinations. Charm System The Charm System is an interrelated group of products that can be