An improved ball valve, in particular for gas systems, includes a tampering indicating seal made by injection molding a synthetic or metal material into cavities formed in the screw-clamping nut assembly and including a cap outer portion which substantially covers the surface of the outer face of the nut andor extending on the side surface of the nut. Two-terminal devices such as passive element memory cells can include a diode steering element in series with an antifuse andor other state change element. The methods of the present invention allow for the production of polys having predictable degrees of incorporation of stereoerrors of a known type.