The ornamental design for the shackle swivel, as shown and described.
FIG. 1 is a top plan view of the shackle swivel embodying our design;
FIG. 2 is a left side elevation view of FIG. 1;
FIG. 3 is a front elevation view of FIG. 1;
FIG. 4 is a bottom plan view of FIG. 1;
FIG. 5 is a front perspective view of FIG. 1;
FIG. 6 is a top plan view of the female threaded collar of the shackle swivel;
FIG. 7 is a left side elevation view of FIG. 6;
FIG. 8 is a front elevation view of FIG. 6;
FIG. 9 is a bottom plan view of FIG. 6; and,
FIG. 10 is a front perspective view of FIG. 6.
The dashed lines in FIGS. 6-10 are not part of the female threaded collar. FIGS. 1-5 show the combination of the female threaded collar and the two clevis components which form the shackle swivel.