Yanmar 3gm30f exhaust hardware ss or grade 8 or something else?

[Eastward ho 24]

Hello. Bought a stainless steel elbow, pipe and mixing elbow from HDI Marine looks like a pretty solid quality product.
.I went on eBay to get four new bolts that attach the elbow to the block they were supposedly Yanmar OEM but they look like they are stainless just seems like a bad place for stainless bolts since they will probab break from vibrating or when I go to remove them again. The yanmar Parts catalogs don't specify what grade of Steel should be used for these four bolts. And my catalog has the old type of elbow that went down. So I can't provide part numbers. I have the elbow type that goes up into a mixing elbow. Also does any one happen to know the thread and size of the outflow of the mixing elbow so I can thread a pipe or hose barb into it? I have a question sent to hdi but maybe some one remembers?

[Chayal]

Is there any numbers on the head of the bolt?

Proper grade stainless bolts are perfect for your application.

Just remember to always a conservative amount of anti-seize.