Today you can go down to your local hardware store an buy bolts and nuts that mate up perfectly well. Most are from China and can be very good and some are absolute crap in tensile strength. Some are real garbage. When you buy that bolt, nut or screw you do not know if it is good stuff or crap.
I wish bolts, nuts and screws were labeled with tensile strength.
Also the chemical composition...and for high tech work...the manufacturing technique...and finally the corrosive potential
They are. Next time look at the markings on the head of the bolt for hardness.
They are. All metric bolts have a number stamped on the head followed by a decimal point, and then a second number. The first number is the tensile strength in thousands of mega-Pascals. The number after the decimal point is the ratio between tensile and yield strength. You multiply the first number by the second to get the yield strength. (Don't confuse the size of the bolt with the strength. A 10 mm diameter metric bolt is generally called an M10 bold. This is NOT marked on the bolt. An M10 bolt can be any strength. A bolt marked 10.8 on the head can be any diameter.)
SAE bolts are a little less specific. There are generally three grades available: grade 2, grade 5, and grade 8. Grade 2, the weakest, has no markings. Grade 5 is moderate strength, and has three radial lines on the head. Grade 8 is the highest strength, and has 6 radial lines on the head. If you didn't notice, add 2 to the number of radial lines on the head to get the grade of the bolt.
Hex bolts are labeled for tensile strength