The ornamental design for a drum key, as shown and described.
FIG. 1 is a perspective view of a drum key.
FIG. 2 is a top view of the drum key of FIG. 1.
FIG. 3 is a bottom view of the drum key of FIG. 1.
FIG. 4 is a left side view of the drum key of FIG. 1.
FIG. 5 is a right side view of the drum key of FIG. 1.
FIG. 6 is a rear view of the drum key of FIG. 1;
FIG. 7 is a front view of the drum key of FIG. 1; and,
FIG. 8 is an environmental view of the drum key of FIG. 1 being used to open a bottle.
The broken lines shown in FIG. 3 represent unclaimed details while broken lines shown in FIG. 8 are for environmental purposes only; the broken lines form no part of the claimed design.