Searching for #12 grade 8 screw

[Tom]

I'm trying to find a 12-24 flat head screw, 2 inches long, in grade 8 hardened steel. They are easy to find in SS and softer steels but I am on the hunt for a grade 8 (or similar) hardened version. If anyone can find a link to one and post it here, I'll waive your membership fees for a full year.

[dr bob]

You've raised my curiosity level a couple notches. What's if for?

Industrial hardware stores usually have interesting stuff like this. And FWIW, a 2" 12-24 machine screw is almost always threaded all the way to the head, and making that tougher doesn't buy a lot with all the threading.

[Tom]

You've raised my curiosity level a couple notches. What's if for?

Industrial hardware stores usually have interesting stuff like this. And FWIW, a 2" 12-24 machine screw is almost always threaded all the way to the head, and making that tougher doesn't buy a lot with all the threading.

After cutting the 928 motor down the middle to make a 4-cylinder motor for the 944, Porsche then strapped Mitsubishi-patented balance shafts to both sides of the motor to make it run smoother. (It is a big 4 -cylinder and Porsche no-doubt studied the Trophy 4 Pontiac 3.2 liter from the early 60's, which was also half of a production V8, courtesy of John Delorean. That motor shook so badly that Pontiac used tiny trampolines for motor mounts trying to keep the shake out of the cabin, but I digress....)

The 944 balance shafts have sprockets on the end for a balance shaft belt (stick with me, I'm getting there). In order to remove those sprockets, Porsche designed a pin-wrench to fit into the sprocket to hold it still while tightening and loosening the bolt holding it on. That pin wrench is about $170.

I, of course, spend my spare time creating weird and unlikely 3D-printed things that others might find useful (since sitting at my computer takes so much less energy and is easier on my knee than real work). Recently, I made a pin-wrench for the 944 balance shafts. That pin wrench uses 12-24 screws as the 'pins.' While torture testing the plastic wrench for its max torque limits, I discovered that my stainless bolts were actually starting to flex and bend before the plastic would fail. I've since "updated" to regular zinc-plated steel bolts, which seemed to help quite a bit, so thought it would be better still to get grade 8 bolts. I just haven't been able to find any.

BSassembled.jpg (992.85 KiB) Viewed 557 times

[Arne2]

Tom, have you thought about using hardened roll pins instead?

[Tom]

Tom, have you thought about using hardened roll pins instead?

Yeah, that's what the factory tool uses too. The design philosophy of my 3D printed stuff is to create solutions that people can make on their own with stuff laying around the garage (or easy to get at any ol' store) so they aren't stuck waiting on UPS packages. Harbor Freight actually sells a roll pin kit with a perfect pin for this, so I might try a version with that. I'd be inclined to heat set them (I.e., heat them up and melt them into a slightly too-small hole), but then people may not get them straight. The beauty of the screws is that they are foolproof from an assembly perspective....

[blueline]

I'm surprised McMaster-Carr (which I learned about from you!) doesn't have what you're looking for but apparently they don't or you would have found them.

What about these Alloy Steel Hex Drive Flat Head Screws from them? According to McMaster they are made from alloy steel and are nearly twice as strong as stainless steel flat head screws.

McMaster-Carr 12-24 flat hed screws screenshot 2023-04-09.png (68.67 KiB) Viewed 523 times

[Tom]

Thanks, McMaster is always my first go-to. Love that place. Order by 4 and its on my porch by 10 the next morning. I did look at those when I first started hunting and wondered how 'twice as strong as ss' compares to the bolts I now have, and the tool does better with fully threaded bolts. I assumed real grade 8 bolts would be easy to find, so kind of forget about those. But so far they may be the most promising yet.

[ROB III]

Tom, I'm making an assumption that since you considered roll pins, thread count is less an issue and diameter is the key.
#12 screw diameter is 7/32, or 0.216 in., or 5.49mm, so 0.5mm smaller than M6.
If the idea is to heat up the bolt to screw it into the plastic, then 0.5mm larger than a #12/24 screw/bolt shouldn't matter. Once in place some judicious filing/grinding could lose the extra 0.5mm.....and grade 12.9 is actually higher than grade 8.
I Googled m6 50 mm long (1.97 inch) grade 12.9 bolt and got a couple hits, one from Amazon.
Do you think this might work or am I way off base?

[blueline]

Thanks, McMaster is always my first go-to. Love that place. Order by 4 and its on my porch by 10 the next morning. I did look at those when I first started hunting and wondered how 'twice as strong as ss' compares to the bolts I now have, and the tool does better with fully threaded bolts. I assumed real grade 8 bolts would be easy to find, so kind of forget about those. But so far they may be the most promising yet.

So, according to McMaster 316 SS = 70k tensile strength psi, 18-8 SS = 80k, and the alloy steel are 130k.

[Tom]

Tom, I'm making an assumption that since you considered roll pins, thread count is less an issue and diameter is the key.
#12 screw diameter is 7/32, or 0.216 in., or 5.49mm, so 0.5mm smaller than M6.
If the idea is to heat up the bolt to screw it into the plastic, then 0.5mm larger than a #12/24 screw/bolt shouldn't matter. Once in place some judicious filing/grinding could lose the extra 0.5mm.....and grade 12.9 is actually higher than grade 8.
I Googled m6 50 mm long (1.97 inch) grade 12.9 bolt and got a couple hits, one from Amazon.
Do you think this might work or am I way off base?

No, you are very much on base... For the threaded bolts, I actually just made the holes a tad small, and the bolts self-tap and screw in very tight. The heat would just be for roll pins if I tried those. I originally did use M6 screws, and they would even work in the model I posted (albeit very tight in holes). The issue is that M6 bolts are about .5mm bigger in diameter than the 7/32 (5.5mm) roll pins in the factory tool. And while they DO fit in the sprocket holes, then end up scraping the edge of the big spacer nut under the bolt. Not a big deal for most, but anyone with freshly plated hardware might get irked. I tried separating the pins just a tad, to cheat them apart so they wouldn't scrape the nut, but then they became kind of a squeeze to get in the sprocket holes. The other issue with M6 bolts is that they didn't fit nicely into the spring tensioner, for those who want to use this tool for that purpose too. So filing them to clear the nut would still leave that issue. So that's when I decided to just use 12-24 screws, even though they aren't all that common....