This standard specifies the properties of the following nuts under the conditions of the conical proof load test. Nominal diameter of one screw d 5 to 39 mm Part class A and B One strength class 8 to 12 Reference This test is specified in JIS B 1042 (Fastening parts - Surface defects Part 2 Nuts with nominal thread size M5 to M39) Used for inspecting surface defects.