What is the difference between a 158 carpenter bolt and one made from 9310 steel? — 1 Answer

The difference is in the steel. Many manufacturers will state that properly heat treated 9310 is approximately 7-8% "stronger" than 158, but 9310 requires that it be heat treated properly to achieve that increase in strength. Carpenter 158 is mil-spec, but many companies nowadays are opting for "stronger" steels like 9310 and S7 which are both tool steels used in large machines. There is a ton of metallurgical information for both steels and you can find the breakdown of both on Carpenter Techology's website as they manufacture both steels. There is also information published by the companies using the steel breaking down the differences more in depth.