The ornamental design for a basemember for airdiffuser, as shown and described.
FIG. 1 is a front perspective view of a base member for air diffuser, showing our new design;
FIG. 2 is a rear perspective view of thereof;
FIG. 3 is a front elevation view of thereof;
FIG. 4 is a rear elevation view of thereof;
FIG. 5 is a left elevation view of thereof;
FIG. 6 is a right elevation view of thereof;
FIG. 7 is a top plan view of thereof; and,
FIG. 8 is a bottom plan view of thereof.
The base member for air diffuser is shown with a symbolic break in its length. The appearance of any portion of the base member for air diffuser between the break lines forms no part of the claimed design.