Abstract: The invention comprises a cap member having an annular wall and a top wall disposed within and connected to the annular wall. An arcuate pierce-plow member is disposed on an upper surface of the top wall at a position spaced from the annular wall. The pierce-plow member includes a first plow base member having a ramp portion and a substantially flat portion. The pierce-plow member further includes a piercing member disposed adjacent to the substantially flat portion of the plow base member. The piercing member includes a first portion disposed adjacent to the first plow base member and a second portion disposed at a position spaced from the first plow base member. A thickness of the second portion of the piercing member is greater than a thickness of the first portion of the piercing member.