Stainless Steel Fastners - Thinking Outloud...

rambos_ride

[hudsonguy]I just bought new stainless steel screws from Totally Stainless. 5/16-24 x 3/4" Oval Phillips Hd. for $0.42/ea. Their part number is 2-3280. I think they're on page 100 of their catalog. Here's their website;

http://totallystainless.net/totally.html

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Nice link BTW!

The thread this response came from made me think this might be a good seperate topic.

I know from building some custom stainless parts for the Hudson that Stainless Steel pipe and sheeting (SS) that it is soft and maleable compared to steel so I have started to question where I use stainless steel fastners in my projects.

Are SS bolts/screws made from SS or coated? I have never thought to ask...because I would wonder about their hardness (2-5 maybe?) and use in certain applications.

For the doors - they're fairly heavy and at least the drivers door gets used a lot ...can you tighten SS Fastners down enough without marring the phillips or allen head to keep the doors in place over time?

What about getting paint to stick to them - for those interested in painted heads?

I'd say you want a grade 5 at least in the hinges - 8 would be overkill, but make me sleep good at night!

Thoughts? Any DIY metallurgists out there?

7XPacemaker

I will say that I kind of like the allen heads due to the positive hold that the keyway has. I kind of hate Phillips head screws. They are destined to strip out too easily....I just talked myself out of the Phillips screws again.........

rambos_ride

An internet search is bearing out some of my thinking...here's some excerpts...

When contemplating replacing OEM fasteners with stainless steel, remember that common stainless steel does not have the strength of common alloy steels and should not be used for critical, highly stressed applications. The stainless steel also has higher friction than steel does which gives less preload at the same torque. When in doubt, keep the OEM steel stuff for critical applications.

This table is simplified but clearly shows SS bolts performing below grade 5 capabilities...

hudsonguy

rambos_ride wrote:

Nice link BTW!



The thread this response came from made me think this might be a good seperate topic.



I know from building some custom stainless parts for the Hudson that Stainless Steel pipe and sheeting (SS) that it is soft and maleable compared to steel so I have started to question where I use stainless steel fastners in my projects.



Are SS bolts/screws made from SS or coated? I have never thought to ask...because I would wonder about their hardness (2-5 maybe?) and use in certain applications.



For the doors - they're fairly heavy and at least the drivers door gets used a lot ...can you tighten SS Fastners down enough without marring the phillips or allen head to keep the doors in place over time?



What about getting paint to stick to them - for those interested in painted heads?



I'd say you want a grade 5 at least in the hinges - 8 would be overkill, but make me sleep good at night!



Thoughts? Any DIY metallurgists out there?[/quote]





Dan,



Well, a DIY metallurgist I'm not, but to answer a couple of your questions; Stainless steel is the material these fasteners are made from, rather than being plated. I've never heard of stainless being used as a plating material. That's usually zinc or cadmium, etc., over steel and other substrates that need corrosion protection.



The screws I bought for my door hinges are comparable to a grade 5. They're probably a type 316, which is going to be stronger than the most common grade 304. After installing them, they look perfect (course, I used a good #3 phillips screwdriver on them) with no marring whatsoever. I wasn't necessarily looking for stainless for these replacement screws, but they were the only ones I could find in that size/head combination....anywhere! I can see how 7XPacemaker had a hard time finding them. This doesn't appear to be a very common size/length.



According to Totally Stainless, they've also got some high strength grades of fasteners that are comparable (or better than) grade 8. I'm sure they probably cost more, but could be used on suspensions and other higher demand applications.

dwardo99

I know from my experience with old motorcycles, that unless a fastener is oversized for its intended purpose, stainless steel is not the way to go on anything that is highly stressed. They are great for certain things that aren't critical but they don't seem to be nearly as strong. The ones that I've used that failed were supposed to be engineered for the application, but they didn't stand up.

hudsonguy

One has to remember that the term 'Stainless Steel' is about as descriptive as the term 'Plastic'. Meaning there are lots of different grades/types, to say nothing of the application variables.



A standard 'off the shelf' stainless fastener is probably rated around 60-70,000 psi tensile strength, about comparable to a grade 2 plated steel. These particular stainless fasteners are rated at closer to 120,000 psi (about grade 5), whereas grade 8 plated steel fasteners are around 150,000 psi tensile strength.



As far as my door hinge screws, I'm confident that these screws I used are more than strong enough for this particular application. I doubt that the original steel screws were as strong as a grade 5, anyway. Not by the way the phillips heads were chewed up over the years.



Stainless fastener threads can be more prone to 'galling', so I used anti-seize on the threads, but I do that with just about any material anyway.

Unknown

as far as paintng ss you would probably have to etch the heads of the screws with some type of etching liquid. before trying to paint them. i just spoke with my brother, he is a machinist, he said that you cant "coat" with stainless. -john