The ornamental design for a nailbrushbase, as shown and described.
FIG. 1 is a perspective view of an embodiment of a nail brush base showing my new design;
FIG. 2 is a side elevation view thereof;
FIG. 3 is another side elevation view thereof;
FIG. 4 is an end elevation view thereof;
FIG. 5 is another end elevation view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The dash-dash-dash type broken lines in the Figures are for the purpose of illustrating unclaimed portions of the nail brush base and form no part of the claimed design.