GB/T 6728-2002 H B 30 20 1.5 3 30 20 1.75 3.5 30 20 2 4 30 20 2.5 5 40 20 1.5 3 40 20 1.75 3.5 40 20 2 4 40 20 2.5 5 40 20 3 6 40 25 1.5 3 40 25 1.75 3.5 40 25 2 4 40 25 2.5 5 40 25 3 6 40 30 1.5 3 40 30 1.75 3.5 40 30 2 4 40 30 2.5 5 40 30 3 6 50 25 1.5 3 50 25 1.75 3.5 50 25 2 4 50 25 2.5 5 50 25 3 6 50 30 1.5 3 50 30 1.75 3.5 50 30 2 4 50 30 2.5 5 50 30 3 6 50 30 4 8 50 40 1.5 3 50 40 1.75 3.5