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Old 30-01-2023, 22:25   #1
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Clevis Pins vs. Bolts

The issue of pins vs bolts to secure rigging came up recently in yet another thread.

A while ago I looked into the strength of stainless bolt vs stainless pin in some depth and could not find evidence that a bolt is less strong in shear than a pin. A reason I often see/hear is that clevis pins are made of a stronger alloy than bolts, but I couldn’t find anything to support that.

I would appreciate hearing solid evidence based arguments why pins are superior to bolts for securing rigging, or vice versa.


As a starting point lets assume:

- Only discussing stainless steel of the same grade, i.e. 304 stainless pin vs. 304 stainless bolt, 316 vs. 316, etc. So apples to apples comparison. If clevis pins of the same grade are truly made stronger by virtue of the manufacturing process, material used, annealing, hardening, etc. then let’s hear why.

- No tensile load. The load case here is clevis pins in shear for connecting standing rigging with little to no expectation of tensile or torsional load. If there’s some reason why a bolt might create or experience something other than shear then please give examples.

- Bolt and pin are the exact same diameter as the hole they are being put into, no issue of point loading due to mismatched radius.

- Bolt shank is the only part under load. No part of the thread is bearing any load whatsoever as it is well understood that the threaded portion of a bolt is not as strong in shear as the shank. How this is accomplished is not part of the discussion (lets just assume it is the case) unless there is an argument that it is impossible to ensure that the thread will not be loaded, in which case I certainly want to hear why.

- No clamping force is exerted by the bolt, i.e. the shank is long enough that when the nut is bottomed out on the thread there is a small amount of space between it and the face of the rigging termination it is securing. Same goes on the side with the head of the bolt, a bit of space, just like you would find if using a clevis pin secured by cotter pins.

- Bolt is free to roll, just like a clevis pin would.


I’m mainly interested in the structural strength question (i.e. is the pin stronger than the bolt) however other reasons or situations why pins are better suited are welcomed.
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Old 30-01-2023, 22:43   #2
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Re: Clevis Pins vs. Bolts

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Originally Posted by Nekton73 View Post
T

- Bolt and pin are the exact same diameter as the hole they are being put into, no issue of point loading due to mismatched radius.

I know that what you mean is "no slop", but as a matter of pedantry, it's not physically possible to put a pin into a hole that is exactly the same diameter as the pin. I'm no machinist but I would imagine you need a few thousandths of an inch difference
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Old 30-01-2023, 23:13   #3
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Re: Clevis Pins vs. Bolts

the bolt is weaker than the pin due to geometry. The thread minor diameter reduces the cross sectional area of the nominal diameter. A pin is ~0.005" under the nominal dia, the larger area is provides the increase in shear / bending.
Now if you use a shoulder bolt that would be closer to the pin in shear, but the nut securing it has a large area reduction at the nut. I would NOT use a shoulder bolt for rigging, they are also expensive for a bolt.
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Old 31-01-2023, 00:23   #4
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Re: Clevis Pins vs. Bolts

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the bolt is weaker than the pin due to geometry. The thread minor diameter reduces the cross sectional area of the nominal diameter. A pin is ~0.005" under the nominal dia, the larger area is provides the increase in shear / bending.
Now if you use a shoulder bolt that would be closer to the pin in shear, but the nut securing it has a large area reduction at the nut. I would NOT use a shoulder bolt for rigging, they are also expensive for a bolt.

Aparently you did not read the initial post thoroughly:

- Bolt shank is the only part under load. No part of the thread is bearing any load whatsoever as it is well understood that the threaded portion of a bolt is not as strong in shear as the shank. How this is accomplished is not part of the discussion (lets just assume it is the case) unless there is an argument that it is impossible to ensure that the thread will not be loaded, in which case I certainly want to hear why.
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Old 31-01-2023, 00:41   #5
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Re: Clevis Pins vs. Bolts

Zero practical difference in strength, the only reason for using pins is due to sizing of the pin length. For any given pin length, a bolt would need to be much longer as you are only using the shank of the bolt.

Other minor reasons, pins are cheaper to manufacture, they weigh less, no threaded nut to come loose, lower profile, look better etc.

If your stuck, cut the thread off a bolt and drill a hole in the end for the securing pin.
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Old 31-01-2023, 01:17   #6
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Re: Clevis Pins vs. Bolts

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Zero practical difference in strength, the only reason for using pins is due to sizing of the pin length. For any given pin length, a bolt would need to be much longer as you are only using the shank of the bolt.

Other minor reasons, pins are cheaper to manufacture, they weigh less, no threaded nut to come loose, lower profile, look better etc.

If your stuck, cut the thread off a bolt and drill a hole in the end for the securing pin.
Not really cheaper. Bolts are made by the hundreds of thousands. Clevis pins - much smaller production runs. Plus, they are made for boats so the prices are higher.

As for weight. Unless you are a racing fanatic the added weight is insignificant, especially at deck level.

The only significant differences are (1) clearance on mast tangs which are placed expecting low profile clevis pins and (2) chafe issues with bolt heads and nuts.
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Old 31-01-2023, 06:09   #7
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Re: Clevis Pins vs. Bolts

Of course if you are using a bolt with only the shoulder engaged in carrying the load, of exactly the right diameter, grade rating, etc. it would be of equal strength to the clevis pin.

The problem is you are unlikely to find a bolt with the shoulder exactly long enough, and threaded part short enough, to work. You could take a bolt with a shoulder more than long enough, cut it to the right length, and cut threads on the end, but what’s the advantage? There are places that I have done this, but they were rather specialized applications, and certainly didn’t turn out cheaper to the client than if a clevis pin could have been used.

I also would not count on a single nylock nut as the only securing in a life safety application, like big boat mast rigging. Others might.
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Old 31-01-2023, 06:47   #8
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Re: Clevis Pins vs. Bolts

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Of course if you are using a bolt with only the shoulder engaged in carrying the load, of exactly the right diameter, grade rating, etc. it would be of equal strength to the clevis pin.

The problem is you are unlikely to find a bolt with the shoulder exactly long enough, and threaded part short enough, to work. You could take a bolt with a shoulder more than long enough, cut it to the right length, and cut threads on the end, but whatís the advantage? There are places that I have done this, but they were rather specialized applications, and certainly didnít turn out cheaper to the client than if a clevis pin could have been used.

I also would not count on a single nylock nut as the only securing in a life safety application, like big boat mast rigging. Others might.
What do you prefer to a Nylock nut? Two of 'em? Two of 'em with red loctite?
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Old 31-01-2023, 07:06   #9
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Re: Clevis Pins vs. Bolts

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What do you prefer to a Nylock nut? Two of 'em? Two of 'em with red loctite?
Think about those places on a boat where failure of a threaded connection is immediately dangerous, or extremely inconvenient. They almost always have a mechanical way of securing the nut from turning. A tabbed washer, drilled nut with safety wire. two nuts jammed together. Cotter pin. Oh wait...

There is ONE place on my boat where a bolt and nylock is used in what I consider a critical application. I don't especially like, it, but I deal. One of the ways I deal is to always use a new nut whenever it has been disassembled.

Depending on your perspective and experiences, I am either very cautious--or paranoid.
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Old 31-01-2023, 12:58   #10
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Re: Clevis Pins vs. Bolts

All the worry about shearing a bolt or clevis pin... I don't believe that I've ever seen or heard of a clevis failing in shear in boat rigging. Failures have always been in the turnbuckle ends or toggles or other such parts, not the pin. And, of course, the pin coming out due to split bin or ring failure or absence ( how we were dismasted in a previous boat).

The pins themselves are damn reliable, and a PROPER bolt (as described) will be equally reliable in shear. And IMO, a Nylock or loc-tited nut in such an application is equally reliable as a pin, and often easier to remove when needed.

The real issue is proper diametric fit, and we've all seen examples of undersized pins in use... and even then, I've not seen one fail in shear, but rather by distortion or damaging the fork by point loading.

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Old 31-01-2023, 16:11   #11
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Re: Clevis Pins vs. Bolts

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Originally Posted by SailingHarmonie View Post
Think about those places on a boat where failure of a threaded connection is immediately dangerous, or extremely inconvenient. They almost always have a mechanical way of securing the nut from turning. A tabbed washer, drilled nut with safety wire. two nuts jammed together. Cotter pin. Oh wait...

There is ONE place on my boat where a bolt and nylock is used in what I consider a critical application. I don't especially like, it, but I deal. One of the ways I deal is to always use a new nut whenever it has been disassembled.

Depending on your perspective and experiences, I am either very cautious--or paranoid.
I guess I see the point of a castle nut on a propshaft, but anywhere there's not that sort of torque, I find one Nylock perfectly safe--never seen one, even one used and re-used, back out. Have you, or is this just a belt-and-suspenders thing?
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Old 31-01-2023, 16:42   #12
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Re: Clevis Pins vs. Bolts

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I guess I see the point of a castle nut on a propshaft, but anywhere there's not that sort of torque, I find one Nylock perfectly safe--never seen one, even one used and re-used, back out. Have you, or is this just a belt-and-suspenders thing?
I have had a nylock loosen. It was on an engine in a high vibration environment, but it showed me it was possible. That left me with a belt and suspenders attitude for things that might fall on my head.

Not trying to sell this attitude, just what I do.
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Old 31-01-2023, 16:59   #13
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Re: Clevis Pins vs. Bolts

It's all good what you write, but as you have pointed out, there is a whole lot of things to go wrong by using a bolt rather than a pin. IE: Inadvertently leaving a small amount of thread taking the load. The nut not bottoming out exactly, not leaving the correct amount of play.
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Old 31-01-2023, 17:12   #14
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Re: Clevis Pins vs. Bolts

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Originally Posted by SailingHarmonie View Post
I have had a nylock loosen. It was on an engine in a high vibration environment, but it showed me it was possible. That left me with a belt and suspenders attitude for things that might fall on my head.

Not trying to sell this attitude, just what I do.
How close was it to the hot bits? Nylon is a thermoplastic after all. And plastics donít melt all at once like ice, they get softer and softer as the temperature rises.
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Old 31-01-2023, 20:43   #15
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Re: Clevis Pins vs. Bolts

Thanks for the input so far. Don't know what I was thinking suggesting a bolt or pin could go through a hole of the exact same size . What's life without a little pedantry.

I too have never seen a nylock come loose, ever, even under some pretty extreme conditions... but I accept that it is possible and respect that for some the risk is just too great. Good to hear that and add it to my considerations.

I'm not quite understanding the comment about cutting a long shank bolt and then re-threading. So far I have always been able to find a shoulder length that fit the application well, although I'm sure there are situations where that isn't the case so it makes sense to just stick with a clevis pin. With a longer shoulder the threaded portion of the bolt is usually way too long and needs shortening, but that is a matter of a couple of minutes with a good hacksaw and file to round off the sharp ends. Once done the ease of nut and bolt has been worth the effort. As is standard practice I leave two threads showing past the nut, although this really is only an issue for tensile loading but it's easily done so why not.

Where I have started using a bolt so far is to attach the forestay at the stemhead. I de-rig almost every year and it is much quicker and easier than the old clevis pin. I have considered switching to bolts for my cap shroud and lower stay attachments at the chainplates but so far have not done so. I've also used them at the masthead for my spinnaker crane and forestay. I had to drop the forestay a few times a couple of seasons ago to deal with some furler issues, and found a nut and bolt much easier to deal with than clevis and cotter pins when dangling from the masthead.




But keep the comments coming. A question that is always in the back of my mind is: nuts and bolts have been around for a very long time so why have builders stuck with clevis pins? What am I missing?
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