Energy Bolting supply fasteners and machined components in ASTM A540/A540M materials. The ASTM A540/A540M specification covers regular and special-quality alloy steel bolting that are commonly used for nuclear and other special applications. ASTM A540/A540M Bolting Grades & Classes B21 Class 1 - B21 Class 2 - B21 Class 3 - B21 Class 4 - B21 Class 5 B22 Class 1 - B22 Class 2 - B22 Class 3 - B22 Class 4 - B22 Class 5 B23 Class 1 - B23 Class 2 - B23 Class 3 - B23 Class 4 - B23 C