The ornamental design for a holder for a medicaltool, as shown and described.
FIG. 1 is a perspective view of a holder for a medical tool showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken line showing of the four circular regions and the rectangular shaped region are for environmental purposes only and form no part of the claimed design.