The ornamental design for a pipette part, as shown and described.
FIG. 1 is a front view of the pipette part showing the new design;
FIG. 2 is a rear view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a top view thereof; and,
FIG. 6 is a bottom view thereof.
The broken lines in the drawing views are included for the purpose of illustrating portions of the pipette part that form no part of the claimed design.