The ornamental design for an airdamdevice for trucks, as shown.
FIG. 1 is a front view of an air dam device for trucks;
FIG. 2 is a back view thereof;
FIG. 3 is a side view thereof (opposite side is mirror image);
FIG. 4 is a top view thereof;
FIG. 5 is a perspective view thereof;
FIG. 6 is an exploded view thereof; and,
FIG. 7 is a front view in uses thereof.
In FIG. 7, the broken line showing of environmental structure for purposes of illustrating the rosary device in a condition of use. The broken lines and the structure they depict form no part of the claimed design.