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View Full Version : bolt types, threads, and hardness/toughness



darryl
01-12-2010, 03:50 AM
I bought some bolts today, SHCS, opting for metric so I could get a relatively fine thread along with a relatively large minor diameter as compared to the outer diameter. I also bought some same thread (M8x1.25) hex head bolts after being told they were not as hard. I needed something like that so I could either cross drill them or machine a hex on one end.

Now I find that the hex head bolts are just as hard as the SHCS. I can work with it, but just a few general questions- For imperial size SHCS, vs grade 8 bolts- is there a difference other than the color and style, and the same question would apply to the metric offerings as well.

If I bought imperial, I could get grade 5 and 8, hex heads, and SHCS. Does that correspond in metric hardware pretty much the same? I guess I should look up a chart showing the head markings for both types, and the equivalencies.

My local supplier doesn't carry imperial NF in the socket head, except for very small sizes, starting at 10-24, where they also stock the 10-32, etc. Is this normal for a machine shop?

small.planes
01-12-2010, 03:55 AM
IIRC most (metric) SHCS are 12.9 grade, with 8.8 grade available.
They are usually marked on the rin of the socket with a number.
12.9 has a higher tensile strength.

someone with more detail may be along in a mo....

Dave

form_change
01-12-2010, 04:50 AM
Metric Hex heads are available in a variety of grades, the same as imperial fasteners are. What you can get will depend on how good your bolt supplier is - more stock is more cost. With slow moving items (odd sizes) it may not be worth his while to carry them. SHCS are not so varied. Colour of the fastener is not a good indicator as it will depend on whether the bolts are black oxide coated, 'bright' or plated. High strenght fasteners can be plated provided they are then treated to avoid hydrogen embrittlement which as the name suggests makes them brittle.
As you suggest an internet search will produce charts with head marking patterns that will help you identify what is what. To find those odd sizes you may have to find a larger supplier that will do mail order.

Michael

darryl
01-12-2010, 04:53 AM
Ok, I lied a bit. The hex head bolts are not as hard as the socket heads. So the guy at the shop did steer me right- Still pretty hard though. Testing with a file, it seems that an imperial socket head bolt is about equivalent to a metric 8.8 bolt, and the metric socket head is harder. I'm glad I didn't try to cut the metric socket head on the bandsaw.

Is there a distinction here- if you're looking for the ultimate strength in a bolt, does that mean you have to go to a metric bolt- or am I just being 'tricked' by seeing only what this metal shop carries in stock?

The question is academic at this point, since it looks like I will be able to work with the 8.8 grade material to make these parts I need. They will be 8mm diameter, 1/2 inch long, and have a hex ground on one end for .1 inch of the length. The hex is 3/16 across the flats- that's as big as I can make it from the minor diameter of the donor bolt. The parts are play adjustors, and there's only a gap of about .1 inch to put the wrench into. My wrench is .090 thick.

oldtiffie
01-12-2010, 05:14 AM
I bought some bolts today, SHCS, opting for metric so I could get a relatively fine thread along with a relatively large minor diameter as compared to the outer diameter. I also bought some same thread (M8x1.25) hex head bolts after being told they were not as hard. I needed something like that so I could either cross drill them or machine a hex on one end.

Now I find that the hex head bolts are just as hard as the SHCS. I can work with it, but just a few general questions- For imperial size SHCS, vs grade 8 bolts- is there a difference other than the color and style, and the same question would apply to the metric offerings as well.

If I bought imperial, I could get grade 5 and 8, hex heads, and SHCS. Does that correspond in metric hardware pretty much the same? I guess I should look up a chart showing the head markings for both types, and the equivalencies.

My local supplier doesn't carry imperial NF in the socket head, except for very small sizes, starting at 10-24, where they also stock the 10-32, etc. Is this normal for a machine shop?

Darryl.

This should help you along the way:
http://i200.photobucket.com/albums/aa294/oldtiffie/Black_book/Black_book2_P44-45_1.jpg

darryl
01-12-2010, 05:45 AM
Thanks, Tiffie. That has pretty much all the info on it that I asked for. According to that, imperial and metric socket head bolts are equivalent, it takes a grade 9 hex head to equal the socket head, the 8.8 metric hex head is equivalent to our grade 5 hex head, and unless a metric hex head can be had in a 12.9, the imperial system has the strongest hex head in the grade 9.

That does it for me, thanks again. I'm dealing with something a little stronger than a grade 5 bolt to make my little parts out of. Fine.

I was almost scared to post here again- I just read the entire thread on 10-24 vs 3/16 :)

Oh, just a note- there's one grade of fastener in both inch and metric that's missing from those charts- that would be the 'assortment' grade, the stuff where the heads twist off before the fastener even gets tight. Well- I guess you can't even call them fasteners. :)

One thing that scares me- it might be that soon you won't know if that socket head bolt you buy is the real thing:(

Paul Alciatore
01-12-2010, 12:52 PM
I don't know what it is like in B.C., but in the states if you go to a local hardware or home supply store you get mostly grade 2. They are just stocking the cheapest as the average Joe just wants to get the cheapest.

Auto parts stores generally stock grade 5, but you usually have to ask for it. They also may have some grade 8 or better for specific purposes and only in the exact sizes needed for that purpose: perhaps part of a kit.

I am in a small town and have to use mail order to get any better hardware, like cap screws. Oh, there are small packages (one or two) of cap screws at the home supply places, but you pay dearly. Far better to get a box of 100 or 50 and pay the postage even if you need only 6 or 10. In larger cities you can find wholesale places that stock a good variety.

Metric is still harder to get here than inch sizes, but that is slowly changing. Auto parts stores are forced to stock it and even the hardware and home supply places have at least some. NF is also harder to find, except perhaps for the 10-32 size which is fairly common. It is much used in electronics for things like rack mounting screws. I buy those by the thousands at work.

wierdscience
01-12-2010, 01:16 PM
So far as stocking most shops even bolt suppliers don't stock both NC and NF in socket head stuff.The biggest reason is cost,it's horribly expensive to stock all sizes in both threads.

Then there is common use,that plays a factor even in low grade hex bolts.Some sizes and lengths are much more commonly used than others.As a result the not so common sizes cost a premium.As an example 1/2-13 x 6" costs less than a 1/2-13 x 5" simply because there are a lot more 6" being used.

At work we stock everything in grade 3,5 and 8 in hex bolts from 1/4-20 to 1"-8 and lengths to 14".Above 1" we go to 2" 4-1/2,but only in the common sizes since above 1" each bolt can run $10 each+

In socket heads we only keep #4 - 1/2-20 in fine thread the rest are coarse.Just not enough call for the larger NF sizes.

Look good at your local hardware stores bins.A standard setup from somebody like Midwest Fastners,just G5&8 to 1" bolts,nuts,washers and bins costs $18,000+ for them to purchase.Worst is most times it's a break even proposition at best since many sales require customer service to find what they need and then they only end up selling a few of a given size.A bolt bin in a hardware store or a machineshop is bascially there to get people in the door and make other sales.Sadly bolt bins are becoming a thing of the past.The big box stores have all gone plastic blisterpacks with poor quality and high prices.

darryl
01-12-2010, 04:05 PM
I feel kind of lucky that I can purchase this hardware at a local machine shop, from the bins that they have for their own use. They do have a pretty good assortment, but it also is the commonly used stuff, so anything odd has to be ordered in. They are pretty good about that as well, and they don't charge an arm and a leg for that service. They do ask that I wait so they can include what I'm looking for with a larger order. I'm fine with that. They also like to make sure that the hardware I'm buying is actually suitable for the project. Nice people to deal with.

By the way, not that this means anything to anybody, but the founder of this shop is the guy who invented the corrugated culvert, used all over the world. So I've been told anyway.