Features 1、Grade 12.9 alloy steel, forged with high‑strength materials, strong and durable. 2、Through high temperature treatment, the screw strength is improved, has a long service life. 3、The thread is clear, the overall thread of the bolts are neat and clear, is not easy to get silky and the force is even. 4、The head are standard hex grooves are not easy to slip and speed up work efficiency. 5、Complete specifications, can meet your use and replacement needs, very practically. Specification Item Type: Concave End Tightening Set Material: 12.9 grade high-strength alloy steel Model and Quantity: 50 x M3 x 3 Concave End Tightening 50 x M3 x 4 Concave End Tightening 50 x M3 x 10 Concave End Tightening 40 x M4 x 4 Concave End Tightening 40 x M4 x 6 Concave End Tightening 30 x M5 x 5 Concave End Tightening 30 x M5 x 8 Concave End Tightening 20 x M6 x 6 Concave End Tightening 20 x M6 x 10 Concave End Tightening 20 x M8 x 8 Concave End Tightening Package List 50 x M3 x 3 Concave End Tightening 50 x M3 x 4 Concave End Tightening 50 x M3 x 10 Concave End Tightening 40 x M4 x 4 Concave End Tightening 40 x M4 x 6 Concave End Tightening 30 x M5 x 5 Concave End Tightening 30 x M5 x 8 Concave End Tightening 20 x M6 x 6 Concave End Tightening 20 x M6 x 10 Concave End Tightening 20 x M8 x 8 Concave End Tightening