What is the best material to use round steel as the U-bolt connecting the sub-frame of the car owner? In detail, 35 steel? 45 steel? 40Cr？

U-shaped bolts are generally Q235-A, and the surface treatment is generally hot-dip galvanized or untreated.

Of course, you have to check the strength, and use round steel with different sizes according to the stress. If the load is large, you want to use small diameter materials.

Then use 35, 45, 40 Cr to see the comprehensive economic value.