Hardware Grade Stuff
Shark_13,
Could be wrong but, I believe the conventional SAE grades are reserved for carbon-alloy steels only and that stainless precludes these from receiving such a rating (such as grade 5 or grade 8), and due to some info gaps, I can't bypass the ratings and use yield or tinsel strengths to provide a 1:1 comparison.
Here are the best answers I've got, though:
Answer 1:
If you are using a winch plate such as this:
https://www.4wd.com/Jeep-Winches-Je...03.aspx?t_c=18&t_s=126&t_pt=3440&t_pn=S/B2803
The plate is going to be secured to the jeep by 4 x 1/2" bolts and the 2 x the bolt(s) that secure the front of the sway bar brackets. Not sure what these are off hand, but they should be at least 3/8". Your winch is only secured down by 4 x 3/8" bolts. Thus, even if you excluded two of the 1/2" bolts from the winch plate, your winch (4 x 3/8") is still going to rip off of the plate before the plate (2 x 1/2" + 2 x ≥3/8") rips off the vehicle. I did some quick math using hardware yield ratings and bolt diameters, and if you secured your winch down with grade 8 bolts, then it should hold 57,000 lbs...I really can't conceive how you are going to apply that kind of force to a winch (tow hooks maybe). Thus, irrespective of what grade equivalent those/my SS bolts are, I feel pretty confident that my winch is secure enough for winching and street parking here in Crooklyn/Brooklyn (I know, not where a jeep belongs. It pains me too).
Answer 2:
-Grade 5 fasteners have a minimum yield strength of 92,000 psi.
-Grade 8 fasteners have a minimum yield strength of 130,000 psi.
-302 stainless bolts, depending on the treatment, can have a yield strength ranging form 20,000 - 95,000 psi. I was unable to confirm the treatment for these bolts, so I can't give a definitive comparison.
Doing conservative math (bolt cross sectional area * yield str. * # bolts):
-the 4 x grade 8 3/8" winch plate bolts will yield at 57k lbs load.
-(2 x 1/2" grade 8's) + (2 x 3/8" grade 8's) + (2 x SS anti-tampers at low end or yield range of 20,000 psi) = bolts will yield at 87k lbs load.
Obviously the above answers aren't perfect, but they seem indicative of a attainment of a good enough threshold. In pursuit of perfection, I spoke to the company that made the bolts I presently have today and they could make true grade 8 versions of these. Producing a lot of grade 8's and the keys would cost over $1k. If there is enough interest from fellow jeepers in having some of these, I might be up for making the investment. With the lot divided up, costs for bolts and keys would probably be similar to what the existing set cost. If anyone would be interested in those perhaps drop me a PM.
There seems to be some suggestion that grade 5 is OK for securing the winch to the plate as the following anti-tamper bolts for that portion of the equation are only grade 5:
Factor 55 Wrangler Winch Lock (Universal Application) 00001-01 - Free Shipping
I used one these to ensure that step of the equation is secure. That said, once the bumper is secured it is next to impossible to get to the bottom side of the winch plate with tools. 1/2 bumper bolts alone probably OK from a security standpoint.
Well, that got overly detailed quickly. I need a hobby or something. Oh wait, that's why we're here