N/A Primary and Secondary Seals prevent line media from contacting stem and body components. The primary seal is formed by an interference fit between the disc hub and the seat flat. The secondary seal is an interference fit between the stem and seat stem hole. Ultraflo's Disc edge is CNC contoured and hand polished to produce zero leakage shut off, minimum torque and longer seat life. Discs available in 316 Stainless Steel, Aluminum Bronze, Nodular Iron and Nylon Coated Nodular Iron. 400 Series Stems are constructed of high strength 17-4 PH Stainless Steel to eliminate twisting and includes industry standard connections for actuator mounting. Upper and Lower Stem Bushings are constructed of heavy duty non-corrosive thermoplastic polymer to eliminate galling and reduce torque. The Upper Bushing also absorbs operator side thrusts and ensures precision alignment. (The Lower Bushing is offered only on 4" and larger valves.) A Stem Packing ensures a positive seal for pressure or vacuum service and prevents external contaminants from entering the stem bore. Body Recesses ease installation alignment and accommodate lightweight flanges. The Top Plate has industry standardized drilling for total manual operator and actuator interchangeability. 400 Series Disc Screws are 316SS as standard and are sealed with Buna-N O-rings to prevent corrosive media from contacting the stem.