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SS Coachscrews at Bunnings - Are they ok? 1-Aug-2014 At 7:10:02 AM Mr Poopypants

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Hey Pat

"A" ratings are just the ratings for the type of stainless used. (and unreliable for strength) There are A, A1, A2, A3 & A4 ratings used, or no rating at all. No rating should be a red flag.

The other number on the head indicates the strength property class of the stainless, not the bolt. Stainless rated in China has been known to be incorrect and suppliers are now cagey about the source. One ring manufacturer thought he had A4 but they are now rusting.

Bolts are also classed for strength. If buying from a large supplier they will offer various classes of strength (eg 8.8 high tensile, ISO or DIN ratings) for different purposes etc.
So, there is a huge variation in their strength ratings. A cheap wood screw is weaker than a roofing hex head screw of the same diameter.

Bolts are not torqued to failure to test them, they are usually straight pulled. Only classed bolts have this done. Cheapies from China etc. mostly don't.

They apparently always break at the thread, regardless of whether machine bolts or set screws (set screws are the ones with thread all the way to the head, as opposed to coach screws).
Classed machine bolts (usually more expensive, but not always), therefore, are classed according to the breaking strength of the thread section (the weakest part).

E.Wells:

So, last time I checked the figures in manufacturers catalogues set screws met the same standards as machine bolts. (the better quality ones I was buying), because they always break a the thread, which they both have. Obviously the machine bolt doesn't have thread where the hanger sits and would be stronger, but both are rated way beyond what you can generate in a fall.

I've spoken to a few engineers from the glue manufacturers (3 different companies) and they all stressed that fully threaded bar is way stronger in the glue due to increased surface area for the dissapation of energy. (I'm no physicist, though.) But that is why I've used some glued in set screws with hangers.
Their strength in shear is way past anything you ever want to generate falling on them.

I'm really not that alarmed at any of this. Glued in bolts are strong, more likely to have problems with the glueing than the bolt. I've just seen coach screws break in some pretty weird places, so I don't like them, even in my decks etc. at home. Batten screws are way stronger.

Hey Michael, I'd hate to see the bolt in the front end of your car that a mechanic could break using 20kg of force on a shifter. Not going to happen. I've got boxes full of 10mm machine bolts you're welcome to try to break using a shifter, if you like. (feel free to put a metre long bar on one) I kinda like the idea of drinking beer and breaking bolts. But maybe you've had a bad experience with some of that Italian engineering you're so fond of??.
:-)

G.

My apologies to all the mechanical engineers our there who are cringing at my simplistic understanding of all this crap. All I am really saying is that bolts aint bolts, Sol. (Brownie points if you know where that quote came from)