The 100761963 Buna-N O-Ring is designed for use with size NW630 ISO-BF centering ring assemblies. This 2-474 size O-ring is made of black Buna-N compound N674-70 and is rated for up to 80 deg. C bakeout temperature. This Series 76 accessory offers seals easier and is less expensive than similar Viton O-rings and can be used as a spare or replacement O-ring.