A system has been devised that utilizes the same head for metric screws having machine and spaced tapping threads . This family of metric fasteners includes Pan, Flat and Raised Countersunk Heads, both Slotted and Recessed and Hexagon and Hexagon Washer Heads.Of particular interest are the analytical approaches taken to develop the designs. A formulation to calculate the torque capabilities of Phillips recesses was used to determine recess depths in all recessed product. Formulae were also developed to calculate recess volumes so that head volumes could be accurately assessed. A computer program employing the Monte Carlo principle was used to calculate minimum material clearance between recess and screw outer surfaces, underhead bearing areas and head material volumes.Included in this report are the complete formulations of all dimensions, design criteria and details of the analytical studies made.