A fastening system for driving fasteners through fastener caps. The cavities may be nested polygonal cavities, for example, having a square or rectangular cross section. The semiconductor memories are mounted on the mounting board. Also provided is an oxygen blending apparatus which utilizes solenoid valves having specific orifice sizes for blending desired amounts of oxygen into the inspiratory gas flow. The contact points are to be in contact with the terminals, respectively. By minimizing or preventing arterial steal, other complications associated with arteriovenous grafts are also avoided.