The ornamental design for a stem, as shown and described.
FIG. 1 is a top perspective view of the stem, showing my new design, a portion of the stein being broken away to indicate indeterminate length.
FIG. 2 is a bottom perspective view thereof, a portion of the stem being broken away to indicate indeterminate length.
FIG. 3 is a side elevational view thereof, a portion of the stem being broken away to indicate indeterminate length.
FIG. 4 is a top plan view thereof.
FIG. 5 is a bottom plan view thereof.
FIG. 6 is an exploded top perspective view thereof, a portion of the stem being broken away to indicate indeterminate length.
FIG. 7 is an exploded bottom perspective view thereof, a portion of the stem being broken away to indicate indeterminate length; and,
FIG. 8 is an exploded side elevational view thereof, a portion of the stem being broken away to indicate indeterminate length.
The broken lines showing thread and thread receiving portions in the stem are for the purpose of illustrating environmental structure and unclaimed subject matter and form no part of the claimed design. The stem is shown with a symbolic break in its length. The appearance of any portion of the article between the break lines forms no part of the claimed design.