The grades of metric bolts are: 4.6; 4.8; 5.8; 6.8; 8.8; 9.8; 10.9; 12.9.
The grades of metric nuts are: 4; 5; 6; 8; 10; 12 where 4; 5 is the strength grade of the thin nut.
So: does it make sense to use grade 8.8 for bolts and grade 4 for nuts?
First: 8.8 and 4 are too unscientific.
Generally, the decimal number after the bolt grade is removed when selecting, which is the grade of the nut. Grade 8.8 bolts are matched with grade 8 nuts, and grade 10.9 bolts are matched with grade 10 nuts.
That is, the strength grades of bolts and nuts are the same (the strength grades of bolt 8.8 and nut 8 are the same, because the ".8" after the bolt indicates that the yield strength is 80% of the tensile strength.), but considering the use situation, if the nut is not Easy to replace, the bolt is relatively easy to replace, and it can also be changed to bolt 4.8 nut 5.
Nuts are somewhat weaker than bolts in some cases. The main reasons are: Bolt failures are usually imperceptible and sometimes sudden, while nut failures are easier to detect. Safety aspects are also considered. In this way, it can be ensured that the life of the screw is longer than that of the nut when used together, and the cost of disassembling and replacing the fastener will be lower and easier.