Dumb question about threads

[Chicken lights]

Ok so I have a dumb question.
So I have six of these on my truck. They cost $30 each to buy. I’ve replaced four but should replace the last two. If I want to make these, I’m sort of confused on what size steel to start with

The rod below the threads measures 0.275, yet the threads measure 0.308.

That can’t be right, I’m guessing these are a stamped part maybe?

It’s just 5/16” NC thread. Nothing special

But how can the outer diameter of the threads be larger than the material of the rest of the part?

 

[ducdon]

Threads are rolled rather than cut. The rolling moves metal upward as it presses in the grooves. Often see rolled threads on studs. Makes a stronger thread.

 

[CalgaryPT]

I always wondered that too...despite seeing threads rolled I never made the connection. Thanks @ducdon

 

[Chicken lights]

Threads are rolled rather than cut. The rolling moves metal upward as it presses in the grooves. Often see rolled threads on studs. Makes a stronger thread.

So I might actually make a weaker part by making my own?
I was thinking of getting a chunk of stainless rod to make a couple of these, I may even have a piece in the shop already

 

[PeterT]

Hard to say. Maybe rolling the threads saves manufacturing cost over cutting threads. Looks like that size is in the order of 4000 pounds tensile depending on the material etc. I'm guessing bolts might be similarly formed vs cut. Most grades of bolts are pretty decent steel. Now how much to deduct assuming its a cut thread vs rolled thread I'm not exactly sure.

 

[Chicken lights]

Hard to say. Maybe rolling the threads saves manufacturing cost over cutting threads. Looks like that size is in the order of 4000 pounds tensile depending on the material etc. I'm guessing bolts might be similarly formed vs cut. Most grades of bolts are pretty decent steel. Now how much to deduct assuming its a cut thread vs rolled thread I'm not exactly sure.

That’s interesting.
I wonder what “4000 pounds tensile” equates to, in something that could cross over to plainer English.
As in, a range in foot pounds for a torque value, or something

I’m guessing what I’ll be using them for, cut threads will be fine. It was neat to get some education on how parts are made!

 

[PeterT]

It simply means you could axially pull on that rod with 4000 pounds (=2 tons) of linear force before the threads themselves would fail. But I have no idea what the part is for, maybe it sees compression force or torque force or some combination - which would typically yield lower numbers. Just pointing out, its a surprisingly big number for some harmless looking grooves we call threads. In real life all sorts of other issues come into play. Maybe he rod bends slightly back & forth or corrosion sets in, which are generally bad for fatiguing any kind of thread. I will go out on a limb & say you are probably fine to replicate them with a decent alloy. As long as they aren't connected to your trailer going up Rogers Pass with the kids inside <eek>

 

[YYCHM]

What function do they serve on your truck? That will determine what kind of load they are under (tension, shear, bending).

 

[ducdon]

I thinks the cutting of threads tends to create stress rizers in the materials particularly at the root of the thread while rolled threads do not. You often see rolled threads on fasteners that are used in high stress repetitive impact service. Main Bearing studs and connecting rod bolts in engines. Disk Brake caliper retaining bolts, etc. A 4000 LB per sq, inch static load is probably a lot less destructive than the repetitive stresses than a connecting rod bolt would see. There's a company called SPS Industries that make very high quality bolts and studs for racing engines. I believe all their products have rolled threads.

 

[ducdon]

It simply means you could axially pull on that rod with 4000 pounds (=2 tons) of linear force before the threads themselves would fail. But I have no idea what the part is for, maybe it sees compression force or torque force or some combination - which would typically yield lower numbers. Just pointing out, its a surprisingly big number for some harmless looking grooves we call threads. In real life all sorts of other issues come into play. Maybe he rod bends slightly back & forth or corrosion sets in, which are generally bad for fatiguing any kind of thread. I will go out on a limb & say you are probably fine to replicate them with a decent alloy. As long as they aren't connected to your trailer going up Rogers Pass with the kids inside <eek>

I think when a tensile strength is quoted for a product it refers to the yeild point of the material not the threads? My metallurgy classes were a long time ago.

 

[PeterT]

Its been a while since I've delved into this stuff too, but here is both tensile & yield for threaded rod. So its entirely threaded.
https://www.fastenal.com/product/fasteners/rods-and-studs/threaded-rods/600173?query=all%20thread&categoryId=600173&level=3&productFamilyId=23394&aggregationSection=true&selectedAggregation=Dia/Thread+Size

I assumed tensile failure stress of a bolt would be across the threads vs. shank because the threads are weaker & will fail first so design to lower number? In shear & other modes maybe they factor the shank because typically you aren't supposed to expose threads in that cross direction? I dunno, time to break out Machinery Handbook.

Back to the original project, how would one roll threads at home even if you wanted to?

 

[CalgaryPT]

Back to the original project, how would one roll threads at home even if you wanted to?

I'm thinking the first step would be to secure venture capital to buy expensive machines. But here's what I learned:

 

[Chicken lights]

What function do they serve on your truck? That will determine what kind of load they are under (tension, shear, bending).

They hold my batteries in place. There’s a flat bar bracket (more or less) that uses three of these to hold down two batteries. One bracket on each side to help sandwich all four batteries together

Besides replacing them when they break, I’m debating adding two more batteries. If I can make my own brackets and hold downs, I’d prefer to do it in-house.

 

[Janger]

Battery hold downs! Easy project. A decent HSS die and long handle die wrench would make it go easier. I would be concerned if it was load bearing. Real bolts are carefully roll formed and heat treated for strength. This project though is simple. You could probably just buy 5/16 ready rod at PA and bend to fit. Put a torch on it till red and bend with pliers.

 

[YYCHM]

They hold my batteries in place. There’s a flat bar bracket (more or less) that uses three of these to hold down two batteries. One bracket on each side to help sandwich all four batteries together

Besides replacing them when they break, I’m debating adding two more batteries. If I can make my own brackets and hold downs, I’d prefer to do it in-house.

I thought they looked familiar. I had battery hold down bolts like that in my 80's F150. They corroded just like yours.

As Janger stated non-load bearing so no real need to make them super strong.

John - do you think powder coating them would alleviate the corrosion problem?

 

[Chicken lights]

Battery hold downs! Easy project. A decent HSS die and long handle die wrench would make it go easier. I would be concerned if it was load bearing. Real bolts are carefully roll formed and heat treated for strength. This project though is simple. You could probably just buy 5/16 ready rod at PA and bend to fit. Put a torch on it till red and bend with pliers.

The only downfall to that idea is the threads on the ready rod would probably chew the aluminum up where it’s bolted to.
Other than that I agree, chunk of stainless rod, bend it, cut threads, go home happy

 

[Janger]

I thought they looked familiar. I had battery hold down bolts like that in my 80's F150. They corroded just like yours.

As Janger stated non-load bearing so no real need to make them super strong.

John - do you think powder coating them would alleviate the corrosion problem?

Yeah I think powder coating would help a lot. If you get acid on it though I don’t think anything would help.

 

[PeterT]

There are these rubberized coatings in aerosol or brush on. I've never tried but intrigued. They say they can be peeled which I can understand would be a useful feature in some applications, but what if you want it to be permanent?

https://www.lowes.com/pd/Plasti-Dip-11-fl-oz-White-Aerosol-Spray-Rubberized-Coating/3851549

 

[CalgaryPT]

That's a great idea. I have used them on tools w/o grips, and they are still there.

My son introduced me to Plasti Dip years ago. You can get it at Canadian Tire. I laughed at first and thought it wouldn't work, but he put it on his first car's rims and when the kidney foundation came and towed the car away 5 years later it was still good as new. No pitting from salt or rock chips. Amazing stuff. It is permanent if you want, but you can also peal it off if needed. Great product!

Comes in spray or dip. I like the spray.

 

[Tom O]

Thats a good idea i'd never thought of that!