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I drilled eight 1/4" diameter holes for mounting my rock sliders and bought stainless steel bolts (1/4-20) to hold them on so that I didn't need to deal with rust. Now I am thinking that was a bad idea because I didn't know stainless steel is weaker than grade 5 steel. Are these bolts going to be able to hold up or are they going to snap when I come down on this slider?
 

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04 Wrangler Unlimited, 67 F100
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I drilled eight 1/4" diameter holes for mounting my rock sliders and bought stainless steel bolts (1/4-20) to hold them on so that I didn't need to deal with rust. Now I am thinking that was a bad idea because I didn't know stainless steel is weaker than grade 5 steel. Are these bolts going to be able to hold up or are they going to snap when I come down on this slider?
I have used a lot of stainless bolts on rock sliders. 3/8 or 5/16 diameter. It depends on your design whether or not they will be strong enough.
 

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Discussion Starter · #3 ·
I put the step rail on and tested by jacking the car up about 3-4 inches (tires were still on the ground) using the step rail and everything seemed solid. But lifting is not the same as an impact load.
 

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I do not own a Cherokee, though I used to work at a Jeep dealership, so, how I look at it is how strong is the unibody compared to the stainless steel bolt. If you used (8) SS 1/4" bolts per side side there should be enough clamping force so the bolts do not break. Especially if you used SS 1" fender washers 1/16" thick on the backside. If you just used normal sized (SAE) washers they might not have enough surface area to prevent a pull through under impact.

I have a Bronco II and if I had put rock sliders on, which I plan to do, I would have used grade 8 3/8" diameter bolts with alloy washers and 3/8" grade 8 nyl-nuts with at least 6 attachment points per side .

Though I think 8 (1/4) SS per side is fine. You can always do a non-destructive test trial before you hit the trails. Jack up the vehicle, lay out CMUs with 2x8s on the top, with the Jeep high enough to be 4" above the wood on the jacked up side, two wheels on the ground on the other side, then drop the floor jack as quick as possible. Then drive forward 2-3". Then lift the vehicle, remove everything, set the Jeep on jack stands, and see if any damage or breakage was done. I would consider a slight denting of the washers fine, but, not the pulling of the bolt through the nut.

imho, Nothing is worse then assuming it is fine, then finding out it is not in the middle of nowhere, because you can't open your doors, because your rock sliders are jammed up against your rocker panels or doors.

Or in my case, my POJ rotted body was so structurally challenged with bad body mounts, I could not get my driver's door closed until I got the B2 back onto a level surface because of the torque put on the frame by the trailer I was pulling through the mud. Luckily I was on my own property.
 

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It depends on the actual stainless material. 18-8, T316 are two common stainless fastener materials and they are equivalent to Grade 5 bolts at 120 ksi ultimate strength. There are some lesser material stainless fasteners which could be as low as 65 ksi. If we assume the worst and you have 65 ksi stainless bolts, the ultimate strength of each bolt can be calculated quickly since you are using 1/4" bolts. The cross sectional area of a 1/4" bolt is calculated from Pi x R squared. R = 0.125" (half the diameter) so they have a cross sectional area of 3.14 x 0.125 x 0.125 = 0.0491 in^2. If they are 65 ksi (65,000 psi) then 65,000 x 0.0491 = 3,192 lb before the fastener will reach ultimate (break). However the yield strength of the lowest end stainless fasteners is as low as 20 ksi. Yielding will cause them to permanently stretch and therefore become loose. The load per fastener to get to yield is 20,000 x 0.0491 = 982 lb. You have 8 fasteners total but not all 8 may be under load at the same time so being conservative you could have only 2 fasteners carry the initial load which means only 1,964 lbs on them before they start to yield. Now I know XJ's are light but not that light. So either you bump up the fastener diameter significantly, verify the fastener material is equivalent to a Grade 5 fastener (which would result in an ultimate tensile strength of 5,892 lb and yield of 4,517 lb Yield strength PER FASTENER) or change fastener material.
If you're worried about rust, do what we do where I used to work and dip Grade 8 fasteners or equivalent in primer before installation. It's called a wet installation. The primer prevents dis-similar materials corrosion and also acts like a locking feature to prevent it from vibrating loose.

Good luck,
Dave
 
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