The ornamental design for a pistonassembly, as shown and described.
FIG. 1 is a front perspective view of the piston assembly shown in a first position;
FIG. 2 is a top perspective view of the piston assembly shown in a first position;
FIG. 3 is a front elevation view of the piston assembly shown in a first position, with the rear elevation view being a mirror image of the front elevation view;
FIG. 4 is a right elevation view of the piston assembly shown in a first position;
FIG. 5 is a left elevation view of the piston assembly shown in a first position;
FIG. 6 is a top plan view of the piston assembly shown in a first position;
FIG. 7 is a bottom plan view of the piston assembly shown in a first position; and,
FIG. 8 is a front perspective view of the piston assembly shown in a second position.
The broken line in FIGS. 1, 3–5, 7, and 8 which define the bounds of the claimed design form no part thereof.