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Which carrage bolt?

tomstractorsandtoys

tomstractorsandtoys

Well-known Member
I am building new door for the one silo. I am using two sheets of 3/4 plywood. My doors swing in on a bracket that is also the step for climbing the silo. The hardware all mounts with 3/8 carriage bolts. My farm supply store has grade two bolts that are plated (says for decks and treated lumber) and they also carry a grade 5 regular carriage bolts. Which should I use? Silage is very corrosive along with the stuff used to treat the plywood but grade 5 is a much stronger bolt than a grade 2. Thanks Tom
 
Grade 5 is a better bolt but will likely only last 40 years or so and need to be replaced again.
 
Good info. In either case the strength is not critical as humans would have a tough time tearing up a 3/8" bolt even if it was soft steel. But the stainless is by far better. Though it too is likely not a hard material (unless way expensive) Jim
 
kind of a what ever question as either bolts will work depending on what you prefer. stainless is ideal but costs more. you can also use neversieze on the coated grade 5.or spray them with paint. wont be a permanent save. grade 2 will probably be black bolts and will rust fast, but if plated go for them.
 
> Let me add to this by recommending you look for fine thread (3/8"-24) rather than coarse (3/8"-16).
> This article explains why my choice would be for fine thread:

Fine thread carriage bolts aren't easy to find. If you have a source please let me know, as I have some on my Ford 4000 that I'd like to replace.
 
> Good info. In either case the strength is not critical as humans would have a tough time tearing up a 3/8" bolt even if it was soft steel. But the stainless is by far better. Though it too is likely not a hard material (unless way expensive) Jim

Common stainless fasteners are 304 stainless, and have a tensile strength of about 70,000 psi, a little better than Grade 2 (60,000 psi). 316 $tainle$$ $teel fasteners are around 80,000 psi and Grade 5 fasteners are 120,000 psi. IMO 304 stainless fasteners have a much more consistent quality than Grade 2, which are generally garbage.
 
(quoted from post at 15:14:30 05/07/20) > Let me add to this by recommending you look for fine thread (3/8"-24) rather than coarse (3/8"-16).
> This article explains why my choice would be for fine thread:

Fine thread carriage bolts aren't easy to find. If you have a source please let me know, as I have some on my Ford 4000 that I'd like to replace.
Click to expand...

I had a bit more in the post originally, but took it away. That part included me saying that fine-thread carriage are impossible to find in my area (maybe special order?), but I know they exist as I have a couple of oddballs in my misc. old bolts bin.

I've never personally needed fine-thread carriage.
 
> Use hot dipped galvanized bolts if you only want to spend 50% vs stainless.

Actually galvanized might be a better choice if they will come in contact with galvanized steel, as there is likely to be galvanic action between stainless steel and galvanized steel.
 
> Here

> https://www.mcmaster.com/carriage-bolts/thread-type~unf/

It looks like McMaster only carries #10 fine thread carriage bolts. My Ford uses 1/4 and 5/16 fine thread bolts.
 
I am 50 so no matter which I use they will last longer than me climbing the silo.LOL I think I am going to use the grade 5 ones. If I did not have an Amish crew coming tomorrow I would look into stainless steel. They called yesterday afternoon and needed work for tomorrow so it was short notice but I did want the job done before first crop haylage goes in. It is a 14x40 silo. Tom
 
Strength is not going to be the issue when sandwiching wood.

I would concentrate on the corrosion resistance.

There are cad plated or light galvanized, which don't give a lot of protection, especially when exposed to corrosive chemicals or worse yet, staying wet inside the wood where the corrosion goes unseen. Not what you want for steps!

Then there are hot dipped galvanized which are much better. Next is stainless.
 
I have been making silo doors for 30 years. Have been working on silo unloaders for over 40 years. That said, a good quality Zink plated 3/8 grade 2 bolt is fine. Just place a 1/2 in flat washer between the bolt head and the wood on the silage side of door. Also glue the two plywood together with a good glue. I screw the plywood together to hold it till glue sets up. The screws will rust away but the glue will hold the plywood.
 
The lumber yard recommended a good glue for between the sheets and sent screws along. Thanks for the tip about a 1/2 washer under the carrage bolt head. Tom
 
Personally I wouldn't give you a plug nickle for any grade 2 bolts in anything other than a shear bolt.

As a mechanic for many years, I could tell you horror stories about cheap junk bolts.

Seen a Reese hitch bolted on with grade 2 bolts pulling a small camper shear off like butter in a month!

Spend the little extra and use grade 5 or better, your life or mine may depend on it?
 
(quoted from post at 15:54:38 05/07/20) I am 50 so no matter which I use they will last longer than me climbing the silo.LOL I think I am going to use the grade 5 ones. If I did not have an Amish crew coming tomorrow I would look into stainless steel. They called yesterday afternoon and needed work for tomorrow so it was short notice but I did want the job done before first crop haylage goes in. It is a 14x40 silo. Tom
Click to expand...


Yes, Tom you will never see any difference.
 
The original bolts were just plain old run of the mill coarse threaded carriage bolts that you'd find in the bin at Tractor Supply. Nothing special about them.

They lasted what, 40 years? I wouldn't overthink this.
 
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