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Fastner material and grades ?

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PSweeney:
On my previous cars I've used mostly Grade 8.8 BZP fastners and over time the corrode and go cloudy white.  I' intend to chrome all my axles and links and was wondering if stainless grades A2 or A4 are acceptable on higher load components such as motor plates, torsion bars, radius rods, steering links, rod end half nut and through bolts ?   Would I be better off using chromed steel nuts and bolts ? problem with these is they do not have markings ?

rooman:
Phil,
     I use NAS bolts on all of my builds. They are plated to military specs, come with full shanks and short threads and are about the best thing readily available. When I first settled permanently here in the US I worked for a well known chassis shop and their practice was to use (as spelled out in their marketing blurbs) "Grade 8 bolts". The problem was that they were using fully threaded bolts to hold the rear end in place. My issue with that is that the threaded portion of the bolt does not totally fill the hole in the brackets so you are relying on the clamping force on the bolt to hold the rear end in place rather than the fit of the bolt through the mounting holes. After enough hard launches the tendency is for either the bolt to "machine" out the id of the holes or the threads to be worn down and neither scenario is good.
   I hate stainless because of the galling issue and chrome plating also has its own issues (hydrogen embrittlement, diameter change on shank etc). Any business that supplies the aircraft industry should have the NAS hardware Or Euro equivalent) on your side of the water.

Roo

Dolmetsch:
I didn't know about NAS bolts (thanks)but also have had great concerns over using the thread portions of bolts for anything other then holding a nut. To that end I often used a longer G8 bolt with a longer smooth shank and chopped the excessive threads off leaving of couse enuf that even if the in the unlikely event the nut came loose it would have to unwind quite a bit before it could fall off.
don

Lorbiecki:
Agree with the stainless comments. If stainless to stainless is used, the use some type of anti sieze compound. Stainless hardware should not be used in high load areas as grade 8 has a much higher shear then SS. Note that there are many grade of SS (304, 316, 406, etc) and each has its use. And, of course, stay away from chromes hardware in any high load situation as hydrogen embrittlement can take place after a time which can lead to hardware failure.

ARP is of course the best you can get and they have the quality control in place to minimize hardware failure. Remember that the way a screw works is that it is deformed (stretched) when tightened. This is where the stress in the hardware is induces. Each type of hardware will react differently when stressed and this is when the failure will take place.

Also, any bolt in a shear position (rear end, 4 link, etc) should have the proper length in which the shank of the bolt (un threaded) is placed into the various bracketry. This means the threads should actually be outside of the mounting bracket (or flush) and the proper flat washer used to insure that the nut does not bottom on the thread.

Good luck!

PSweeney:
thanks guys, I always use bolts with the appropriate shank, only ever use machine screws into castings.   

Roo, how well does the plating hold up on the NAS bolts and what finishes do you get on them ?  I'm happy that bolt sizes are sufficient for the load, I'm just loathed to spend a fortune on chroming then use black oxide or bzp fastners which corrode.   Fpund one place in the UK doing NAs bolts, one 3/8 UNC 2" bolt nearly $10 :o

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