what about stainless bolts that have " T H E " on them ...that is what came with everything i ordered from KE as well as IMCO .

is that a certain manufacture?

That's the catch. "Proper strength". Grade 2 strength is suitable for fastening a cable bracket to a bulkhead, but really not for anything on an engine. I have one in my shop now that had the crank pulley attached with 3 3/8" stainless bolts. It took less than a month for them to shear. Not much on an engine is fastened by the OEM's with anything less than Gr5's. Even intake manifolds, carb studs, etc.

This shows the ASTM and SAE bolt head markings. Beyond this, they would not be classified fastners. Many companies make specialty bolts that do not fit into any specific classifications. Rod bolts are a good example- they're significantly stronger than something like a Gr8 but aren't classified.

The examples that these guys use to not use stainless are true. Stainless does not do well under shear stress like crank pulleys but like I said, my Merc 500HPs came from the factory with stainless bolts on the intake, exhaust and most of the accessories and I still use SS on the exhaust, (your original question) and have not broken one ever (since 2000) with my twin engine Thunder.

I have good results with with the CMI exhaust manifolds using the ARP SS studs. About $100 an engine but it sure makes a cumbersome install easier....like the SS manifold w/twins for a right hander!

To reiterate- there's nothing wrong with using the CORRECT stainless bolt for the application. The trick is getting the correct one. I have no direct knowledge of what Merc uses but past experience tells me they're not 300-series. Take for example the studs on a Merc gimbal. Those are a hardened stainless, not something you'd find at Lowe's

I would use L9 cad plated bolts. Get them at your local industrial fastener or bolt supply. Had them holding cast iron manifolds with turbos on top for 14 years. Ive pulled them dozens of times never had a problem with L9 bolts very strong industrial bolt. The problem with stainless 308 or 316 there is no carbon. 400 series stainless has a little carbon so its a little tougher. But stainless will strech and fatiuge over time. 28 yr job shop machinist.

I AGREE WITH CHRIS SUNKIN MY BUDDY USE WRONG BOLT ON STARTER HE SNAP IT IN HALF THE BIG DUMMY HAD TO PULL THE MOTOR TO GET TO THE BOLT