Capri Tools 419 Piece BUNA-N MM Universal O-Ring Assortment Metric, 32 Sizes 32 SIZES: This O-ring assortment set can cover all your needs with 419 pieces distributed across 32 sizes HEAVY-DUTY: Not your basic rubber, Buna-nitrile (Buna-N) is specially formulated to resist penetration at (70a durometer) DURABLE: Buna-N is also proven to endure the test of time with incredible long-term durability HIGH STANDARDS: These O-Rings comply with aerospace standards AS568A CONVENIENT HARD CASE: These 407 O-Rings come in a convenient carrying case for storage and portability