a horizontal elongate rigid bar having an elongate axis, an upper edge, a lower edge, a front side, a back side, a first end, and a second end;

four jaws depending from and below the bar, the jaws having a jaw length measured from the lower edge of the bar to the farthest point on the jaw from the lower edge of the bar;

the first jaw fixed to the first end and extending below the bar;

the first jaw further comprising a first jaw face;

the first jaw face lying in a plane perpendicular to the axis and facing the rear end;

the second jaw extending below the bar, and slidably mounted on the bar between the first jaw and the rear end by a means for releasable positioning of the second jaw;

the second jaw further comprising a second jaw face;

the second jaw face lying in a plane perpendicular to the axis and facing the first jaw face;

the first jaw face and second jaw face being separated by a variable first spacing depending on the position of the second jaw on the bar; and

a double jaw assembly comprising the third jaw, the fourth jaw, and a slide having a top edge, a first end and a second end;

the slide comprising a rigid elongate member slidably mounted on the bar between the second jaw and the second end by a means for releasable positioning of the slide on the bar;

the third jaw mounted on the first end of the slide and further comprising a third jaw face;

the third jaw face lying in a plane perpendicular to the axis and facing the rear end;

the fourth jaw mounted on the second end of the slide between the third jaw and the rear end and further comprising a fourth jaw face;

the fourth jaw face lying in a plane perpendicular to the axis and facing the third jaw face;

the third jaw face and the fourth jaw face being separated by a second spacing.