11/16 is not a common bolt size. In fact it pretty much doesn't exist. Bolts are measured by the diameter of the outside of the threads and not the head of the bolt. Sounds like you probably have a 7/16" bolt.
Bolts are rated in tensile strength in the units ksi. That is thousand PSI. You will typically see the "yield" strength ratings. That is when the bolt fails. So the rating the of the bolt is based on the minimum force it takes to yield, or in other words break. These things are measured if you were pulling the bolt from end to end. When you act sideways on the bolt you are looking at the shear strength. This is complicated but if you assume that shear is 60% of the yield (remember we are talking force to break the bolt) then you will get pretty close.
In SUPER basic terms SAE, read that "american", bolts have three basic classifications. These are called grades: grade 2, grade 5 and grade 8. These are MINIMUM specs that must be met in order to be graded that way. The bolts are made from differing metals and have different heat treatments applied to them to achieve the various hardness and strength ratings. Grade 2 is the weakest, cheapest and most common. It is typically a chinese made bolt sold in an american store. These bolts are typically marked with "307A or "A307" on the top of the bolt head. Grade 5 and Grade 8 are both harder bolts. They are marked with radial lines on the top of the bolt head. Grade 5 has three equidistant radial lines and Grade 8 has 6 similar lines.
On bolts the length of the thread is standardized. So if you see a 3" bolt with 1.75" of thread then the 5" bolt will also have 1.75" of thread. I don't need to get into the length formula here.
The nuts that go with these fasteners are rated for similar forces. So if you are using grade 8 bolts you should be using grade 8 nuts to achieve maximum strength. If the bolt is threaded into something of unknown tensile strength then the total strength of the unit is questionable and can't be identified unless you have an engineering analysis and testing done.
I haven't touched on other grades of metal. There are two grades of stainless that are widely used in fasteners: t304 and t316 stainless. These bolts have a lower tensile strength than SAE hardened bolts. I have seen test results as high as 120ksi, which is comparable to grade 5 SAE bolts, but typical analysis is 50-70ksi and more in line with grade 2 fasteners.
Another problem with stainless is that it galls easily. You need to use a thread lubricant when assembling the bolts. Galling is basically pressure welding two pieces of stainless together. If you have TONS of money to kill then you should send your stainless fasteners out to be Xylon coated. This acts as a thread lubricant so you can avoid adding something at time of assembly.
If you happen to be working with a pure chloride environment and you don't need to weld the stainless then I would suggest Duplex 2205 stainless. That is some blinging stuff!
I'll try to attach a MTR tomorrow. That is a Material Test Report provided by the manufacturer for each lot of bolts. They are pretty neat.
