Assortment O-Rings come in a convenient resealable plastic case. Kit Contains 18 popular O-Ring sizes. Hydrogenated Nitrile Butadiene Rubber (HNBR), also known as Highly Saturated Nitrile (HSN) is special class of nitrile rubber (NBR) and is for mission critical applications. HNBR can be formulated to meet application temperatures ranging between -45 degrees C and 165 degrees C. HNBR is classified by ASTM as DH-type polymer This 270 piece HNBR o-ring assortment kit contains 18 popular sizes: (20) 7/32 x 1/16", (20) 1/4 x 1/16", (20) 6.8 x 1.9, (20) 5/16 x 1/16", (20) 7.8 x 1.9, (20) 8 x 2, (20) 8.8 x 1.9, (15) 7/16 x 1/16", (15) 7/16 x 3/32", (15) 11 x 2 , (15) 12 x 2, ( 10 ) 13.9 x 1.8, (10) 9/16 x 3/32", (10) 14 x 2, (10) 15 x 2, (10) 17 x 2, (10) 11/16 x 1/16", and (10) 11/16 x 1/8".