We claim the ornamental design for a lug nut spike cap, as shown and described.
FIG. 1 is a bottom perspective view of a lug nut spike cap, showing our new design;
FIG. 2 is an exploded bottom perspective view thereof, illustrating a lug nut exploded away from the lug nut spike cap;
FIG. 3 is a front elevational view thereof, the rear elevational view, left-side elevational view, and right-side elevational view all being identical thereto;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a cross-sectional view thereof, taken along line 6-6 of FIG. 3.
The broken lines showing a lug nut in FIGS. 1 and 2 depict environmental matter and form no part of the claimed design.