The ornamental design for a screwhead, as shown and described.
1. Screw head
1.1 : Perspective
1.2 : Side view
1.3 : Side view
1.4 : Bottom
1.5 : Top
1.6 : Perspective
Fig. 1.1 is a perspective view of the screw head; fig. 1.2 is a side view of the screw head; fig. 1.3 is a side view of the screw head; fig. 1.4 is a bottom view of the screw head; fig. 1.5 is a top view of the screw head; fig. 1.6 is a perspective view of the screw head; the dotted lines form no part of the claimed design.