Standard Pack = 1 piece(s). 419 Piece Metric O-Ring Assortment Contains:; Constructed of Buna-N BG715(Nitrile 70 Shore) Rubber; Meets ASTM D-2000 SAE 200 Standards; (20) 3 x 1.78; (20) 4.40 x 2.62; (18) 5 x 2.62; (23) 7 x 1.78; (23) 10 x 1.78;