D-shaped element consisting of two sections pinned together at the sides by alignment pins on one section (the cope) fitting through eyes on the other (the drag). The pins are not secured. Exterior of the flask has rounded surface and interior is slightly concave. Each section is fabricated of a single iron strap which is bent back on itself at the base and then curves into a round section before folding back on itself at the other side of the base. There is a single 11 mm diameter hole at the top rounded section of the coupler that is shared between the two sections.