What Grade are Stainless Bolts

[Crumm]

Just like the title asks what grade are they? Are they as tough as a grade 5? I twisted one off the other day while working on my boat winch project and got to thinking that they might not be up to the task at hand. I have a bin full of grade 8 bolts but I don't really like the idea of using anything other than stainless in this environment. Anyone know what grade the Stainless would be?

In a google search I found

When contemplating replacing OEM fasteners with stainless steel, remember that common stainless steel does not have the strength of common alloy steels and should not be used for critical, highly stressed applications.

Would a winch mount be highly stressed

But I also found

Inch Grade/Material/Tensile Strength/Yield Strength

Grade 2 / Steel / 510 / 74,000
Grade 5 / Steel / 827 / 120,000
Grade 8 / Alloy / 1030 / 150,000

Stainless / 690 / 100,000

Looks to me like they are way better than a grade 2 but not quite as good as a 5. Is that right? When I twisted one off it was because the threads were buggered from tapping it through a misaligned hole. It took a quite a bit of pressure on the wrench to snap it but not anything like it takes to snap a grade 8.

Thoughts??

 

[powerboatr]

we used stainless bolts in many high stress attachments, like main trannies in helicopters.
the key is get a bolt designed for the application. 1/4 carbon steel bolt and a 1/4 ss bolt, the ss will fail long before the carbon steel
if you need a grade 8 strength .... then your going to need a bigger ss bolt but it will not corroded as fast....

 

[Crumm]

The winch was attached to a ATV using four 5/16 grade 5 bolts. I have it bolted in the boat with four 3/8 SS bolts. The mount is also behind a aluminum brace on top and against the hull on the bottom so it could not really be pulled out even if the bolts broke. I am just more curious than anything on the rating of stainless. You think a 3/8 SS is close to a 5/16 grade 5 as far as strength?

 

[powerboatr]

those 3/8 will probalby stretch the threads pretty good right before they snap,
is the winch rated for 1500 lbs?
i would step up to 7/16 if weight and space allows, plus some large flat washers ,
i cant run faster than a winch flying at me launched from a taught cable

 

[Crumm]

Rated at 2500. It cannot get out no matter what.

Here it is in the compartment:

Here is the front side:

If it comes out of there it hitting me in the head would be the least of my worries. But I still don't want broken bolts. I will put some 7/16 on my shopping list

 

[powerboatr]

yep it would have a heck of a time jumping out of there, whats under it, did you put a plate under the boats metal to spread out the load or is there bracing already incorporated in the design?

 

[Crumm]

On top there is a cross brace that supports the top of the bow. The mount is right up against it and it will take most the pull. On the bottom of the mount it is just supported on a piece of 2"x3" flat bar in two spots(you can see it in picture)with rubber in between it and the 3/16 aluminum hull. This is the same area where the front bow eye is attached and it will support the whole boat in a hard pull.

 

[powerboatr]

sounds like it should work, guess i could have used one down there in florida a time or two across a few sand bars