Zook is the only company in the world devoted exclusively to the development and production of impervious graphite rupture disks. It was Zook who first tested graphite disk venting capacities to ASME specifications to give users the best available flow rates for sizing. Zook is capable of producing graphite disks to ultra low burst ratings. We established fast immediate shipment from stock of over 100 rating and diameter combinations, produced a standard line of 1/2 " miniature diameter graphite disks, tested disk performance at elevated temperatures, and provided burst ratings determined by coincident temperature tests to conform to ASME Sec. VIll Div. 1 code language.