The ornamental design for a half-round base window component, as shown and described.
FIG. 1 is a front elevational view of a half-round base window component
showing our new design, the rear plan view being flat;
FIG. 2 is a bottom view of the half-round base window component of FIG. 1.;
and,
FIG. 3 is a right side elevational view of the half-round base window
component of FIG. 1, the left side elevational view being a mirror image
thereof.