The ornamental design for a mop top, as shown and described.
FIG. 1 is a top perspective view of a mop top;
FIG. 2 is a bottom perspective view thereof;
FIG. 3 is a front view thereof wherein a back view is a mirror image of the front view;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a left view thereof wherein a right view is a mirror image of the left view;
FIG. 7 is a perspective view thereof on a mop or broom; and,
FIG. 8 is a perspective view thereof detached from a mop or broom.
The broken lines in FIGS. 7 and 8 depict environment that forms no part of the claimed design. The broken lines in the FIG. 4 depict a portion of the mop top that forms no part of the claimed design.