Stainless Steel Screw Standards

[jerryspoolman]

I purchased a large quantity of #8 stainless steel screws from BOLT DEPOT, to replace screws in my 14 year old
5th wheel. Most of the original screws had severe rust problems. Even screws that were covered with plastic trim, the heads were
OK, but the tips had rusted down past the threads.
When I tried to use the screws, I had terrible results with the heads stripping out and 1 just snapped. I had only used 5 screws, then
I realized that it would be foolish to replace approximately 300 screws with junk.

The new stainless steel screws could be picked up with a magnet.

Having had good luck with Graingers on other products; I decided I would check their web site. The following is a sample of 2 screws they offer:

Stainless Steel Tapping Sheet Metal Screw
with Pan Head Type and Plain Finish
$23.55 pkg of 50


Stainless Steel Tapping Sheet Metal Screw
with Pan Head Type and Plain Finish
$14.05 pkg of 100

The first screw is priced at $.47 per screw, while the second screw is priced at $.14 per screw.. The Descriptions are identical and there are others
priced between those two. How can I determine which screw is the proper value?

Any advise would be helpful

[CA_Traveler]

Slownsy wrote:
I don’t know about galvanic corrosion but I used stainless steel bolts to hold my aluminum angles on roof and solar panels together and no problem, installed 2 yers ago.
Frank.

X2 Going on 4 years. Believe I used 18-8 SS but not home to check.

FWIW I buy packages of 100 from Bolt Depot. Plenty of extras for the next project and great prices even with S&H.

[free_radical]

pauldub wrote:
And nobody mentioned galvanic corrosion because of the dissimilar metals. Nothing is much worse than stainless in contact with aluminum.

What material bolts or screws would be ok to use with aluminum to prevent galvanic corrosion??

[Slownsy]

I don’t know about galvanic corrosion but I used stainless steel bolts to hold my aluminum angles on roof and solar panels together and no problem, installed 2 yers ago.
Frank.

[Almot]

SidecarFlip wrote:
If they are slightly magnetic, it's 308 stainless.

It can also be 316 or 18-8/304. Slight magnetism is not a definitive method to tell the grade.

[down_home]

Pull one of the good screws and locate a good wholesale parts shop that sells stainless fasteners.
They lost the philips head cap screws to the panels in my water bay and substituted smaller self tapping sheet metal screws.
panels were fall out into the bay.
In Ft Smith after half a day found a wholeseller. He didn't have thephillips head but had hex head self tapping screws. They were not real shiny like chrome but they fit perfectly in the holes the others came out of.
In the wet bay they do occasionally get wet but no rust. I had to buy a hex head bit to fit my 1/4 in socket or screwdriver. It has a magnet in it and it held them. There is stainless steel and stainless metal of varying grades. Someone here more familiar with the various alloys, without consulting a book or the net can shed better light on the subject. Some stainless steel alloys do not rust very easily at all.
I paid, I think 14.00+- for a dozen screws and the bit.

[Chum_lee]

www.boltscience.com

Chum lee

[pauldub]

And nobody mentioned galvanic corrosion because of the dissimilar metals. Nothing is much worse than stainless in contact with aluminum.

[Gjac]

The three most common forms of SS are Austenitic, Martensitic and Ferritic. If it was magnetic, soft and cheap it was probably the SS. Ferritic. Martinsitic is usually harder and is magnetic also. Sometimes they are referred to as 300, 400 or 200 series SS. You want the 300 series like 304 or 316 because although softer than 400 series offer the best corrosion resistance. There are other alloys like Duplex or Precipitation hardened alloys but they are not common.

[time2roll]

Seems to be a lot of iron in stainless.

The most common stainless steel is the 304 grade with 8% nickel and 18% chromium and the balance iron. This is used for such common items as spoons and forks, saucepans and kitchen sinks. Where extra corrosion resistance is required, such as for roofing in marine applications, type 316 is used. This has about the same amount of nickel and chromium as 304 but with 3% of molybdenum added. The balance is again iron.

https://www.azom.com/article.aspx?ArticleID=2194

[RinconVTR]

EDIT. I found SST hardware right on my desk was able to be picked up by a magnet.

[ktmrfs]

time2roll wrote:
Only iron is magnetic.

uh... NO! cobalt, and nickel are also magnetic at room temperatures and there are other magnetic elements. Some have a curie temperature (the temperature at which they transistion between magnetic and non magnetic) below room temperature

[mike-s]

time2roll wrote:
Only iron is magnetic.

Only iron, and nickel, and cobalt, and ...

[SidecarFlip]

If they are slightly magnetic, it's 308 stainless. I use 308 all the time because it machines easily and I make stainless parts. 308 is just as corrosion resistant as other grades plus it's more malleable.

If the screw threads are rusty (the old ones) you have issues other than rusty screws, you have water intrusion under the skin.

[time2roll]

Only iron is magnetic.