FIG. 1 is a perspective view of a base for a rail insulator showing a first embodiment of my new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a side elevational view thereof;
FIG. 5 is a perspective view of a base for a rail insulator showing a second embodiment of my new design;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is a side elevational view thereof;
FIG. 9 is a perspective view of a base for a rail insulator showing a third embodiment of my new design;
FIG. 10 is a top plan view thereof;
FIG. 11 is a bottom plan view thereof; and,
FIG. 12 is a side elevational view thereof.
The parts shown in broken lines in FIGS. 1-12 form no part of the claimed design.