The ornamental design for an extrusion, as shown and described.
FIG. 1 is an isometric view of an extrusion showing my new design;
FIG. 2 is an enlarged perspective view thereof, showing a detail of the grooves;
FIG. 3 is an end view thereof;
FIG. 4 is an enlarged elevation view thereof, showing a detail of the grooves;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is a front elevation view thereof; and,
FIG. 8 is a rear elevation view thereof.
The extrusion is shown with a symbolic break in its length. The appearance of any portion of the extrusion between the break lines forms no part of the claimed design.