A hairpin shaped tool that springs open and when closed has long blades that are parallel about 12-15" long used for shaping glass. All parts of the tool are used by skilled glass workers, but the blades get the most use closing in the narrow neck of the piece on the pipe and working the opening of lips. Blades may be nearly knife edged or rounded. Jacks are also made to hold round (replaceable) paper or wood "blades" Jim Moore is considered to make the best in the US, about $150; the Itallian Dino is supposed to make the best in the world, $250, buy through Pilchuck.
A tool with two metal arms joined at one end by a handle. The distance between the arms is controlled by the glassworker, who uses jacks, or pucellas, to form the mouths of open vessels.