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OT: Question for metal experts


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I have just bought some 316 stainless steel eye-bolt fixings for my boat.

How would an M12 thread 316 grade stainless bolt compare in tensile strength compared to, say, mild steel stud bar and 8.8 grade high tensile bolts of the same size? I guess it will be somewhere in between but just wondered, and I am sure one of the learned engineering types on here will know the answer :)

It probably won't matter because I suspect they will be stronger than the transom on the boat regardless, but was just curious.... just in case I ever have to tow something off them in an emergency.

Ta :)


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ISO property class 4.6 bolts:

Yield stress ~ 240 MPa minimum

Tensile strength ~ 400 MPa minimum

ISO property class 8.8 bolts:

Yield stress ~ 640 MPa minimum (sizes M5 to M16)

Tensile strength ~ 800 MPa minimum (sizes M5 to M16)

I don't have properties for stainless steel bolts. The following is what I found with a quick look.

18-8 stainless steel, condition wrought, work hardened:

Yield stress ~ 650 MPa

Tensile strength ~ 1200 MPa

I realise this does not concern your application, but for others examining the figures quoted above, I would not substitute 8.8 bolts with stainless if strength is an issue.

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Thank :)

somewhere towards the 8.8 strength seems likely then .... ultimate strength isn't the issue but they have to be marine stainless anyway due to being low down on the transom of a boat in salt water - anything else won't last 5 minutes - just wondered how strong they would be. The transom would probably let go first :unsure:

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