Bolt indication method

The representation of bolts includes information such as thread type, material, surface treatment and strength grade. For example, the representation of ordinary threaded bolts is "M6×30", which means ordinary threaded bolts with a nominal diameter of 6mm and a length of 30mm. High-strength threaded bolts have increased the strength grade on the basis of ordinary threaded bolts. The representation method is "M6×30×3.6", which means high-strength threaded bolts with a nominal diameter of 6mm and a pitch of 3mm, and a strength grade of 4.6. Self-locking threaded bolts have increased the self-locking performance on the basis of ordinary threaded bolts. The representation method is "M6×30×3.6 ST", which means self-locking threaded bolts with a nominal diameter of 6mm and a pitch of 3mm, and a strength grade of 4.6.