Doco Overboard
Ultimate Member
Not Salisbury but Billy Warren in Greenwood has all kind of industrial fasteners metal working stock and who knows what else you may ever need in that dept.
Grade 8's are hard, but brittle, and Chinese grade 8's are trash. Do not buy based on grade 8. Choose by advertised and tested strength (ksi) value.Look for Grade 8 Screws.
Hell it's all good. I believe it was you that told me in another thread for an AR 308 set screw gas block that carbon is like clotting blood. Plus I've got a dimple jig now.
I was researching for suppressing a 300blk and adjustable block was the first thing I saw along with an article from pew pew tactical discussing the different types of blocks and the merits of set screw and clamp. I ultimately went with clamp style because of equal pressure around the barrel and a supposed better gas seal. NOW I'm thinking that even though that may be true of clamp gb's, the hardware goes through more stress when tightening. Not only do the screws have to clamp, they also have to DRAG somewhat don't they? If thats the case then it's no wonder that they're snapping the way they are.
Grade 8's are hard, but brittle, and Chinese grade 8's are trash. Do not buy based on grade 8. Choose by advertised and tested strength (ksi) value.
I believe there is a minimum elongation in the SAE spec for gr 8. Gr 8 usually means min 130 ksi yield / 150 ksi tensile. Tensile strength and hardness correlate extremely well. Brittleness and elongation to failure negatively correlate perfectly since brittleness is not a real value.
With no policing or penalties. SAE is not a .gov agency, nor do they have legal/arresting powers.
It should be noted as well, that quality fasteners will also have better geometry to reduce stress concentrations. Rolled instead of cut threads, threads that stop before the head, shanked, (Threads should never be put in shear), generous radii under the head, made from forged vs. cut blanks, etc. A fastener needs to be more then just strong. It needs to resist cyclical loading, bending, corrosion, galling, heat cycling, extreme hot and cold (think Titanic) , etc.
The more expensive bolts will have the grain structure oriented in the proper direction, running continuous along its length and through its geometry changes.
Strength can be achieved in different ways (Heat treating, metallurgy and geometry). You can have strength without brittleness.
Just a side note, the FAA does not allow grade 8 fasteners anywhere near aircraft (maybe one or two non-critical locations). Never minding the lack of true quality control, you do not want to use a fastener that as the first sign of overloading, is catastrophic failure. No warning, no indicators, just bang, your dead. Well designed hardware will bend before it breaks. Brittle hardware will not.
As any engine builder can tell you, they never use grade 8 on anything important... head bolts, bearing caps, and such. They work fine for holding on water pumps, but most racers would not even use them there... because they are brittle, fail without warning and will fail at the most inopportune time.
Grade 8 hardware has been around for years and is widely used. It is generally used where they are never subjected to really high loads on any one bolt. The loads can be shared over a pattern of fasteners. Use them at a max loading of 30% of break strength and you will be fine. But when weight, and size (the gun fasteners of OP) are limitations, and you will be taxing the limits of the fastener, go with a well engineered one. Just realize that the USGov has put out a number of warnings on the quality of imports, which covers 80% of the Grade 8's.
Carroll Smith has a great book on the topic. My copy is over 20 years old.
https://www.amazon.com/Fasteners-Plumbing-Handbook-Motorbooks-Workshop/dp/0879384069
Stanley Dzik, pricey, but considered a bible on the subject,
https://www.amazon.com/Aircraft-Hardware-Standards-Manual-Engineering/dp/0879940123
The FAA has a number of notices warning about fastener problems and the supply chain if you care to dig through them.
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