Clevis Pins vs. Bolts

[HeywoodJ]

Look at it from a different perspective, a round pin shackle (a shackle with a clevis pin for the shackle pin) is the only common shackle type NOT allowed in overhead lifting. Screw pin and bolt/nut/cotter pin shackles are allowed. The reasons are different, a clevis pin shackle can’t support any axial load, the other types can, and with lifting it is hard to ensure that you will always have shear loads.

The takeaway is that the bolt/nut/cotter pin is preferred because it supports both shear and axial loads. If you feel comfortable that no cotter and some other nut securing method are sufficient then the bolt works fine in shear.

[Benz]

^^About your last question: clevis pins present a lower profile at both ends--a cotter pin takes less room than a nut, and as we've seen, securing a nut from rattling off takes either a nylock, which were not always available and still aren't in bronze. Where lower shrouds attach to tangs, often a pin is placed through from the outside, and a cotter pin wiggled in really close to the mast where a nut wouldn't fit.
A nut is really meant to tighten down and put some tension on the bolt: a clevis pin is better, or at least good enough, when you're not really trying to squeeze something.

[Jolly Roger]

Just to add another experience to this discussion, which I do not expect anyone else has ever encounted...
On a recent very roly-poly passage a cotter pin sheered, allowing the clevis pin to pop out of the gooseneck connection on my fore course yard. The whole yard then lurched wildly, to and fro, 35 feet above the deck. I found a cotter pin on deck with one arm missing.
How I stopped the yard is of little importance here, since nobody else has a yard and a squaresail on their boat.
I subsequently repaired the connection using the same diameter bolt, a washer and nylock nut, which I am now much more confident about.
This taught me that wherever there is need for a clevis pin to permit a connection to pivot, and therefore move even a tiny bit laterally, it should be secured with a nylock nut.

[Recy]

Nothing is bullet proof.

[pcmm]

Originally Posted by Recy

Nothing is bullet proof.

Something is odd about that picture. The toggle failed due to the cotter pin shearing, but the pin is still in the Clevis? and the Clevis is hanging on an angle in the tang/forestay fitting. I think here the pin was undersized as a component of the failure.

[Benz]

Originally Posted by Recy

Nothing is bullet proof.

Nothing built wrong, for certain, but it's obvious that that pin is too small for the holes. Fit should be snug.

[Siberian Sea]

I suppose you could always use a flat washer to take some space that would in a way adjust the length of the bolt so that no part of the threads are under load. Also you can get stainless 316 bolts with different grades like grade 4 through 8. Myself I just use the pins but if needed would not hesitate to use a proper sized bolt for a time until I could find the correct pin. I oversized all my rigging connection points by several sizes anyway. Yes, it was topside weight and some extra cost but.... in not a racer and at least in my mind reduced points of failure under normal usage. I’m no expert salty dog and I’ve screwed up once or twice so I need the extra margin of security

[Bill_Giles]

Originally Posted by ChrisOwens

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

You are no machinist. There are specific ‘fits’ such as ‘clearance’ (ie slides in and out easily). Interference - need help going in (hammer, machine press etc) and transition which is somewhere between (close tolerance). This subject has pages and pages to explain it. We boaters are unlikely to meet anything other than a clearance fit unless we are rebuilding engines.

[Agprice272]

Could you cut threads on a clevis pin? Not being silly, but besides the difference in alloy, a bolt and a pin of the same material should be the same strength. Thus, if you want to secure the pin with a nut, could a pin be threaded?

[Goodxcharly]

You could use a bolt.

Double nut it I guess and hope for the best.

I used a long stainless shackle on my back stay so I could attach other random lines. Mast is still up!

[kubota]

corrosion.
clevis pins are finished and surface passivated
on all exposed dimensions.

bolts have threads which are a corrosion weak point.
dont know of any boats that have the required
tools and chemicals to polish and repassivate the surface after cutting so sizing is difficult.

angle grinder/dremel heats the material which
removes hardening and causes chromium precipitation.

mechanical cutters followed by tapping is just mutilation of good stainless.

hack saw is just that, 10 million microscratches in chromium layer.
so buy the right size to start if you use bolts in critical applications.

in operation:
galling from the passage of nuts on and off. breaks the chromium surface and accelerates corrosion. (galling is not necessarily the forcing of the nut, it happens a little with every passage of the material).

trapped seawater in threads deoxygenates and prevents stainless from regenerating its cro2 coating at which point you might as well be using plain steel.

a purpose built fastner like a clevis, properly made, is going to be way more reliable than a kluged in bolt.

as a true paranoiac, i will substitute the cotter in a clevis with a small diameter shoulder bolt and nylock of sufficient length so that the threads arent buried in the clevis hole.

these phenomenon apply to all stainless steels though
316L is more resistant to heat precipitation when cutting with power tools and repolushing.

anecdotally, i was delivering a 42ft from bermuda to hilton head. got caught in an early season hurricane.
the boom sheared off the traveller in a squall and started trying to flog the rig outta the boat. the owners roller furling was useless in that situation (why i dont own one). after lassoing the boom with a line with green water on deck from heel trying to part me from vessel we got things back under control and sailing again with control lines on cleats. ashore some 9 days later (slow sailing with docklines as a boom) over a steak dinner at hilton head i presented the owner with the boom car. u guessed it, some idget had replaced a clevis with a threaded bolt which had corroded and sheared. darn near killed me. pay for the proper
stuff on a boat.

[dlj]

The ease of producing a clevis that will give full diameter strength is much faster to build and install than a properly sized shoulder bolt with nut. Given the original premise of "everything being a perfect fit" (simplified) you are missing the geometry problem. The clevis pin is full diameter all the way through the entire coupling with a head on one side that is not very thick, and the end sticking out on the other side only has to be long enough to put a cotter pin (or similar) through it. The loading is happening cross the full diameter pin and extending beyond the fittings. Both sides can be made to not sick out very far. This geometry is often very desirable.

Now, let's look at the shoulder bolt with a nut. Where do you end the threads to hold the nut? To be equivalent to the pin the threads must stop beyond the connection. Then, you must have enough threaded portion to put the nut onto it. This makes this side stick out further then the pin equivalent. Now you can use low profile nuts but this is getting complicated. If your application doesn't mind the added protrusion - then they are really the same strength. How far out to you make the threaded portion? This all gets more complicated that just using a pin with a hole in the end of it. If the threads do not stick out beyond the fitting - you do not have the same strength as a pin.

Oh and someone said "We boaters are unlikely to meet anything other than a clearance fit unless we are rebuilding engines." I've done a fair amount of work on boats where you can't tolerate a clearance fit - mostly in rudder systems. In those cases you use a taper fit. You have a special tapered pin and the hole is a matching tapered hole so you can drive the two together and there is no slop at all. But these are complicated to build.

dj

[Talbot]

If you are worried about a nylock coming un-done, you could always reinforce with a dab of loctite - colour in accordance with degree of paranoia

[Icarus]

Originally Posted by Nekton73

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.

Pins are a lot cheaper to manufacture than bolts., the tensile strength is the same.

[michaellael]

I have had a clevis pin related failure. Some clevis pins are forged - and the forging process produces a slightly out-of-round shape that point-loads the rigging-end tangs, eventually becoming cracks in the tangs and then failure. I am personally certain that an exactly round shape would not point load and would not develop cracks and failure. The extra metal in a forged pin is overly offset by the shape distortion - my observation of a head-say failure.