The Vac-u-lock Plug is a replacement part for the Doc Johnson Vac-u-lock harness system. This plug can be used with any toy in the Vac-u-lock line and it snaps securely into the Vac-u-lock series harnesses, holding the toy and harness firmly in place. While not much of a toy on its own, this plug is absolutely invaluable to making the Vac-u-lock system work, and it never hurts to have a spare.