Form: This specification and its associated detail specifications cover phosphonitrilic fluoroelastomers (FZ) in the form of molded rings. Application: Primarily for use in aircraft fuel systems operating from -55??o +150??(-67??o +302??. The cross section of such rings is usually not over 0.275 inch (6.98 mm) in diameter or thickness. Classification: Rings are classified by hardness as shown in the detail specifications. Safety-Hazardous Materials: While the materials@ methods@ applications@ and processes described or referenced in this specification may involve the use of hazardous materials@ this specification does not address the hazards which may be involved in such use. It is the sole responsibility of the user to ensure familiarity with the safe and proper use of any hazardous materials and to take necessary precautionary measures to ensure the health and safety of all personnel involved.