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12.9 Bolts are stronger yet.
Yes, but overkill for most applications, and more costly. Having said that, I use Class 12.9 for the front and rear upper plinths (the "camber bolts"), but even 10.9 are an upgrade over the bolts Lotus used there before about 12 yrs ago when they switched to 10.9

-Ed
 

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@Jetblast thanks for your explanation. Should we stick to stainless or titanium? What do you recommend? I will soon change all the suspension bolts in my car and I want to make sure I use the best quality.
Lotus specified property class 10.9 bolts in this particular application and that should be sufficient, I think the key is using quality hardware with the correct corrosion protection. I have not been able to find if Lotus specified a specific corrosion protection treatment for their hardware.

I would stay away from stainless steel for this particular application due to their lack of strength, I believe they are similar in strength to property class 8.8 metric and Grade 5 standard bolts. Titanium hardware is typically very specialized to specific applications and I would not recommend using it unless an engineer with specific knowledge has recommended it for an application since titanium doesn't play well with many types of dissimilar metals.

Black-oxide alloy steel bolts should be avoided due to their lack of corrosion protection. Zinc-plated bolts provide good corrosion protection in wet environments and zinc-flake-coated hardware provides about 20 times more protection than zinc-plated bolts, and zinc-aluminum-coated hardware is about 40 times as resistant to corrosion than standard zinc-plating. The zinc-flaked-coated and zinc-aluminum-coated hardware can be hard to find in certain sizes and grades.

When I sourced hardware for mine I went with a zinc-plated property class 12.9 bolt, mainly due to availability. I would have used zinc-plated property class 10.9 bolts if I could have found a quality source that didn't require large quantity purchases or long lead times. The plating process, if not done properly, can make embrittlement more likely, and higher grade bolts are inherently more susceptible to embrittlement due to environmental factors, so I plan on re-inspecting the bolts every 2 or 3 years.

Sorry for such a long-winded anorak response, I hope this explanation didn't frustrate or confuse you. I just wanted to put some information out there for others to see or comment on.
 

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@Jetblast Thanks for your detailed response. Where did you source your bolts? I purchased the suspension refresh kit from a "known vendor" and the quality of the bolts is quite disappointing, with grades mixed of 10.9 and 12.9...
 

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@Jetblast Thanks for your detailed response. Where did you source your bolts? I purchased the suspension refresh kit from a "known vendor" and the quality of the bolts is quite disappointing, with grades mixed of 10.9 and 12.9...
It can be hard to find some metric hardware with the right dimensions and property classes (in the US at least), I can understand why a kit of hardware might be a mixed bag different grades. I purchased property class 12.9 bolts for this but I would have preferred 10.9 since they should have plenty of strength and in this application, they would be less prone to embrittlement.

I purchased these bolts from McMaster-Carr, they were the first reputable supplier I found that had the bolt specifications posted and the range of sizes I needed. In the past, I've found McMaster-Carr to be a little higher-priced than some of their competitors, but their prices for these bolts were quite reasonable, I'll include links to the ones I purchased.

https://www.mcmaster.com/90128a289
https://www.mcmaster.com/90128a291
https://www.mcmaster.com/90128a292
 

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McMaster-Carr is a good option. 10.9 grade bolts in the sizes we need are very difficult to find in USA. Whenever I place an order with Eliseparts.com or another UK/Europe Lotus supplier I always ask them to add 10.9 grade bolts as they are freely available. I get enough for a few years at a time and most of them have a bolt refresh kit which is good quality and reasonably priced.
 

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Here is one argument about the Higher grade being more brittle --- according to this author its not so.
I agreed, higher grade bolts are not more brittle, they have a higher Rockwell hardness, there is a difference. All other factors being equal, quality made higher grade bolts have higher yield strength, are harder and are not as 'brittle' as lower-grade bolts.

What I meant when I mentioned embrittlement is related to the hydrogen embrittlement which can happen during manufacturing if protocols are not followed or if corners are cut, embrittlement can also happen due to environmental exposure. Hydrogen embrittlement can cause the sudden failure of a bolt below its designed yield strength, similar to what many Elige owners have experienced.

Here is a 2-page article that explains it better than I can...

http://www.boltscience.com/pages/the-stronger-the-better-is-not-necessarily-the-case-for-fasteners.pdf
 

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Interesting that this thread is now re-inventing everything that the thread was originally created for. Including sourcing 12.9s with the correct coating (with links), then back to the 10.9 discussion... now replayed again in the last 5 or so posts. rotfl
 

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It can be hard to find some metric hardware with the right dimensions and property classes (in the US at least), I can understand why a kit of hardware might be a mixed bag different grades. I purchased property class 12.9 bolts for this but I would have preferred 10.9 since they should have plenty of strength and in this application, they would be less prone to embrittlement.



I purchased these bolts from McMaster-Carr, they were the first reputable supplier I found that had the bolt specifications posted and the range of sizes I needed. In the past, I've found McMaster-Carr to be a little higher-priced than some of their competitors, but their prices for these bolts were quite reasonable, I'll include links to the ones I purchased.



https://www.mcmaster.com/90128a289

https://www.mcmaster.com/90128a291

https://www.mcmaster.com/90128a292

The 2nd link is appropriate for the bolts in question in this thread, yes?
 

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The 2nd link is appropriate for the bolts in question in this thread, yes?
Yes, there are three sizes of bolts required for the car, an M10 x 40mm and M10 x 60mm for each side front, and 2 M10 x 50mm for each side on the rear. The middle link above is for the rear bolts.
 
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