I bought some M8 x 25MM stainless steel torx head screws from bunnings. Cheap around $1 each.
Question, can I trust the strength of 304 stainless compared to the normal 316 stainless.
I read that the 304 is more partial to rusting, but at $1 each i can throw out if this starts occurring.
I'm more concerned about the 304 stainless screws possible strength and cracking.??

It's an alloying difference only. The actual physical properties would vary so little I would not bother worrying. IIRC google says tensile strength is the same

I'm my experience, a lot of hardware store 304 stainless in the US is weak, porous, brittle junk.
Once reason to prefer 316 from a known good source...

Most of my stainless Torx screws are from Bunnings, zero problems. I even go as far as bringing off the security tit. Cheap and easy to buy.

+1 Bunnings 304 stainless bolts
been using their T30's in my F-One foil for a year, no issues, no rust.

just cut to length, deburr, perfect. not bad for less than a dollar a pop

www.bunnings.com.au/pinnacle-m6-x-35mm-stainless-steel-security-bolts-8-pack_p2421023

I would not worry about alloy in an M8, M6 I'd consider looking for something like 316.

^^^^ why?

Not sure on the Bunnings bolts but usually Stainless bolts you'd buy from a fasteners store will be marked either A2-70 or A4-70 on the top. A2 = 304 Stainless, A4 = 316, the 700 designation means they meet a minimum of 700MPa ultimate tensile strength....IE they are both the same strength wise.

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Mark _australia said..
^^^^ why?

M8 has many times the strength including thread contact.

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Mark _australia said..
^^^^ why?

Like Grantman said M8 are many times stronger than m6 and for years M6 bolts have worked without failure on masts to board connection so your kind of already ahead of the game. I think most hardware failure of m6 bolts in our hobby comes from over tighten them, more so than from mechanical stresses. and some bolts are just poorly made. Most 304 bolts i see seem to just be general use and can have poor quality control, a I don't trust them ether.

That said, good bolts have ratings for strength, shear and tension loads. All the different ratings can be confusing A2 vs A4 (A4 being stronger) or 8.8 vs 10.9 vs 12.9 (12.9 being more than twice the tensile strength of 8.8)

mechanicalelements.com/stainless-steel-bolts/
Mc master Carrs designate their stronger counter sunk dolts as Torx 'high strength" but at least they actually list the actual tensile strengths!
www.mcmaster.com/products/bolts/flat-head-screws-2~/stainless-steel-torx-flat-head-screws~~/

I know that. The point is grant said is he had M6 he would use 316. That's how I read it.
304 is same strength at 316 as I mentioned before. So a thin bolt does not necessitate using 316

Same strength (in theory) but significantly less corrosion resistance. I've seen a few snapped M6 that had a micro crack which corroded.
That said I prefer M8 for everything except stabilizer connections.

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dkeating said..
I bought some M8 x 25MM stainless steel torx head screws from bunnings. Cheap around $1 each.
Question, can I trust the strength of 304 stainless compared to the normal 316 stainless.
I read that the 304 is more partial to rusting, but at $1 each i can throw out if this starts occurring.
I'm more concerned about the 304 stainless screws possible strength and cracking.??

Tried the rust a bit.

304 is ok as long as you rinse in fresh. My outboard motor is bolted on with 304 bolts and they are fine after years. The grade of bolt strength is relatively independent of the alloying composition. Although 316 is slightly stronger than 304.

You can get A2 (304SS) and A4 (316SS) in various strength grades. It's actually the second number that tells you the strength. A4-50, A4-70, A4-80. The second number means tensile strength in MPa x10. A4/A2-50 is the standard.

So in summary wash your bolts and pay more attention to the second number if you are worried about strength.

I've used the 304s from Bunnings for a couple of years no probs
There slightly softer than the 316 but softer is less brittle which is good with impacts like the reef
And that's probably the most likely time you may loose a foil
Yes they do rust a bit where the torx part is but you should be changing them yearly or sooner anyway