FIG. 1 is an isometric view of a screw head according to the design;
  
    FIG. 2 is a side view thereof;
  
    FIG. 3 is a top side view thereof;
  
    FIG. 4 is a bottom view thereof;
  
    FIG. 5 is an enlarged side view of FIG. 2 with a portion of the screw environment removed for ease of illustration;
  
    FIG. 6 is an enlarged bottom isometric view with a portion of the screw environment removed for ease of illustration; and,
  
    FIG. 7 is another enlarged bottom isometric view with a portion of the screw environment removed for ease of illustration.
  The broken line portions of the screw head illustrate portions that form no part of the claimed design; the broken line showing of the screw body illustrates the environment of the claimed design and forms no part thereof. The dot-dash broken lines define the bounds of the claimed design and form no part thereof.