Strength rating of stainless steel/galvanized bolt

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This has been my life long question that has never gotten answered. On a regular bolt they put markings on the head, but on a stainless steel and galvanized bolts they don't seem to put the same rating. Anyone have an answer? Thanks.
 
Most hardware grade stainless is 18-8 and will be somewhere equivalent to a grade 5 in strength. there are many other grades of stainless that are available as specialties for specific applications but usually not available in general fastener sales. Anything is possible if you have enough quantity and $$$
Galvanized is simply a coating, most used on grade 2 items but could be used on higher grades. The fasteners have to be made to different specs to account for the thickness of the galvanized coating.
 
With regard to aircraft hardware vs hardware store:

AN bolts (such as an AN4) are garden variety aircraft bolts
AN bolts (such as an AN4) made of CRES (corrosion resistant steel) (stainless) are designed to meet the exact same specs.

All AN Bolts meet minimum Tensile Strength Values of 125,000 PSI
Commercial Grade 8 Bolts Have a Comparitive Strength of 150,000 PSI
Commercial Grade 5 Bolts Have a Comparitive Strength of 120,000 PSI
Dropping to 110.000 PSI for Diameters Greater Than 1-Inch
Commercial Grade 2 Bolts Have a Comparitive Strength of 70.000 PSI
Dropping to 60.000 PSI for Diameters Greater Than 3/4"

The reason I bring this up is that "hardware store" 18-8 stainless or even marine stainless can be as low as 20,000 PSI depending on quality. Though it is much more typical to see hardware store stainless at 65,000 PSI tensile strength.
 
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The only thing I would use Stainless on is something non critical. They do make a hardened stainless but it's not common and you wont find it in a regular hardware store. I like Cad plated if I need corrosion protection.
 
As usual, this knowledge was gained the hard way. I used a garden variety 3/8 stainless bolt as the pivot on an alternator. Tightening it up, it sheared. I was beginning to think I would grow old and die under that darned Jeep before I drilled it out. Lesson learned. No more stainless. When I part out a BMW, I save every nut and bolt. The hardware is mostly cad plated. or phosphor coated. Makes the stuff holding the Rat together look like junk.

PS when drilling stainless go very slowly and use tons of oil or you will blue the drill bit and ruin it.
 
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Reason I ask is on my boat trailer they used a standard zinc plated grade 5 bolt to hold on the leaf springs and the front and rear cross members. These are heavily corroded. I'm putting new leaf springs on and would prefer something other than a zinc plated bolt
 
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Should I just go with a cadium plated grade 8? I'm just don't want to be cutting these off in 3 years of salt water immersion.
 
Originally Posted By: SHOZ
I use a lot of 316 stainless. Especially for exhaust where I use a SS bolt and a hardened regular steel nut. SS on SS and exhaust will sometimes gall.


Why don't you use common brass nuts designed for exhaust systems instead?
 
Originally Posted By: motor_oil_madman
Should I just go with a cadium plated grade 8? I'm just don't want to be cutting these off in 3 years of salt water immersion.


I do an ANNUAL inspection of my boat trailer,
and replace any fasteners that need replacing on a yearly basis if needed.
 
Originally Posted By: Linctex
Originally Posted By: SHOZ
I use a lot of 316 stainless. Especially for exhaust where I use a SS bolt and a hardened regular steel nut. SS on SS and exhaust will sometimes gall.


Why don't you use common brass nuts designed for exhaust systems instead?
I have a quantity of the correct metric hardened nuts from the local farm store, buy them by the pound. Brass in metric threads are not common here.
 
Originally Posted By: motor_oil_madman
Reason I ask is on my boat trailer they used a standard zinc plated grade 5 bolt to hold on the leaf springs and the front and rear cross members. These are heavily corroded. I'm putting new leaf springs on and would prefer something other than a zinc plated bolt


If your spring shackle's zinc coated as well I would put back in what came out so you don't get galvanic corrosion. Boat trailers are high maintenance due to the harsh environment they live in.
 
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