Just trying to plan ahead to attach the running board brackets to the frame for the '25 coupe. Since they're hidden anyhow, the thought was whether I should use 'Grade 8' bolts, (or a lesser grade)? After researching, just have a concern if Grade 8 might be too brittle and subject to breaking. Any experience or suggestions appreciated. Thanks.
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Grade 5 would do the job but it is getting hard to find fine thread grade 5 anymore.
I would not hesitate to use grade 8.
I am wondering where you get the idea that grade 8 bolts are brittle.
If I were going to do this job with bolts I would clamp the support to the frame then drill and tap the whole assembly so the bolt pulls the parts together and add a lock washer and jam nut on the inside. Grade 5 should be fine. I thing the rivets would be softer then that. I have done it this way a couple of times on other things. Best yet would be rivet.
I'd purchased grade 8 bolts for this. When I had put them in place to tighten, some of the bolt threads were already rounded off. That is what initially raised my concern. With a need to tolerate 'flex', then to question if tensile strength and shear strength are comparable? (We know glass is hard, will tolerate some flex, but it's also known it will shatter!) I'm just trying to prevent a future problem, while realizing I am often accused of "over-building"... It's a "safe or sorry" question.
A local farm supply store has a good selection of bulk hardware. Here's one of the charts I had referenced:
Marv, button head set screws will do the same job, with the added bonus that with a dob of bog in the hole, they will closely resemble a rivet to the casual observer.
Allan from down under.
Allan, bog is hard to find here in the states. He may have to use epoxy or bondo to fill the heads.
Unless you shop at a well known industrail supply are you really getting grade 8 bolts?? A good quality grade 5 should do but be careful where you buy them!For a time high grade bolts were a easly counterfited item by the same sort as horrible fright! Bud in Wheeler,Mi.
There is a Buckheit hardware store in my area that sells screws, nuts and bolts by the pound regardless of grade - that should tell you something.
If it's a real grade 8, it will break alright. As soon as you load it to 150,000 psi.
I didn't want a 'loaded round to go off' while driving down the road! Whether the bolts may be counterfeit or not, the ones I'm seeing have the appropriate markings and colorization.
Marv, the counterfeit bolts had the appropriate markings and colorization too. That's what made them counterfeit. It used to be a pretty common problem back in the eighties, don't know if it still is. By the way, I don't have any specs to look at, but I think a grade 2 bolt has about the same strength as a rivet, both are pretty much mild steel, as I recall. I could well be wrong though. Dave
The running board brackets were attached with rivets, not bolts!
Grade 2's have an ultimate tensile strength of 74,000 psi in the sizes we are discussing here.
As Larry has written, proper fastener for the running board brackets are rivets. Rivets on the frame are best installed hot. There are several old threads about how to do this. But it sounds like you want to use bolts. Regarding the difference between bolt grades and effect on hardness and strength, any grade bolt will be harder than a hot rivet. Grade 2, 3, 5, 8, and 9, either fine or course thread, will do the job. There is absolutely no scenario on a model T where you need to be concerned about bolt heads violently failing with a bang. Ford used fine thread a lot, fine thread at times with lock washers, but more often with castle nuts and cotter pins or safety wire, I believe, because of the vibration shaking the cars apart. In model T days nuts and bolts were like so many other early and growing technology, learning as they went. Early bolts were not the quality we expect now. Ford drawings I have seen for bolts did not specify a hardness. I did a lot of research for the front spindle bolts as I was unsatisfied by the quality of the spindle bolts being sold by the usual suppliers at that time, in particular, the thickness, which at that time and maybe still, were machined at .5" dia (or less) where the Ford drawing specified a number slightly larger than .5". The Ford drawing calls for the bolt to be made from round steel stock with the end enlarged by drawing it down to form the bolt head. Again no hardness specified. I had several original Ford script spindle bolts analyzed by a certified test lab and was surprised to find the rockwell hardness measured was less but close to a modern grade 2 bolt. A hot rivet will not be as hard as a grade 2 bolt, but it will fill the hole where as a bolt will need clearance space to slide in without damaging the threads, and the threads cut will bring the actual diameter down further still, much smaller than the rivet size, so you trade off strength vs dia. As to the hardness difference by bolt grade on brittleness, we are nowhere near the hardness scale where any grade bolt will shatter more than another. Hardness in a bolt will affect its stretching when tightened, and its susceptibility to wear from friction. Stretching and friction are not concerns with most bolt applications in a model T, certainly not a concern with running board brackets. If you are bound and determined to bolt the running board brackets on any grade bolt, fine or course thread will be adequate. The direct impact to you is cost and availability as you will pay more for fine thread and more for a grade 5 and more for a grade 8 and of course even more for a grade 9.
As I have probably lost most folks interest in the post some time ago, I will say that for those who have stuck with me this long I would like to tell you that Fastenall (that as you might guess sells primarily nuts and bolts) is closing out their grade 9 nuts and bolts. They are mail order too on the internet. They are selling their grade 9's for less than the price of a grade 2's at the local big box store. I cleaned out my local Fastenall store of all its fine thread grade 9 nuts and bolts for my model T, farm tractor, and implements. Warning, grade 9 nuts are taller and may not meet with some folks sense of original appearances, bolt heads are the same.
Grade 8 also has to do with the fit of threads also.Years ago at Olds Millwrights as instructed would install grade 8 bolts in conveyor turn wheels then also have the nut's welded on. From time to time these welded bolts would break and others would still hold the wheel solid.At the time [3rd shift] it was a gravy job to replace broken bolts and weld them only to have them brake again!!!! If i need anything special instead of buy the pound,i go to Alma Bolt and get a good grip on the checkbook!! Bud in Wheeler,Mi.
Grade 8 bolts have fallen from my favor over the years, based on personal prejudice rather than science........so it's good for me to see everything on this post.
I used two 3/4" grade 8's for the lifting pins on a pump jack years ago.....my only source for pumping water. They worked fine for about two weeks and then I heard a snap, followed by a horrible clatter. I ran over and shut down the engine, then found that one of the bolts had snapped off cleanly right at the beginning of the threads. A close examination showed that the metal appeared crystallized, a sure sign of fatigue caused by repeated stress. I replace both with grade 5's and had no trouble after that.
As a result, I have used more "forgiving" fasteners and reserved the grade 8's for high strength-no motion applications.
There was a time when the hardware stores were getting bolts that were just junk and unknowingly they were selling them as grade 8 when they were not even grade 3, or 2.
I canít remember when that was or where they came from.
They had the right color and looked like they were quality bolts.
I think that is why some folks think grade 8 bolts are brittle.