Shackle bolt size

[Kryptonight]

I'm not sure if this is proper place to ask but I know no one that knows anything close to this topic.

I'm fabricating a trailer hitch recovery shackle insert. 2"x2" cold rolled solid square bar stock to insert into my trailer hitch. I'll have a 5/8" cross pin hole drilled in it to secure it to trailer hitch on one ton, 8000lb diesel truck.

My plan is to attach a Crosby G2130 shackle to the end for vehicle recovery when stuck in mud or to pull tree stumps out of ground etc etc. I won't buy Chinese prefab models made by warn etc etc.

My issue is this. The typical shackle is 3/4"
4-6 ton rated. The drill hole needed to attach them is .89" and the opening between the shackle legs is 1.25". So typical Chinese imports grind down the 2x2" bar (usually hollow tube in their case) to 2" x 1.25". Bolt hole wall thickness approx .55" X 1.25" wide or across top.

My thought was to use a 12 ton 1 1/4" shackle which has a 2" opening between the legs. So no stock removal on the 2x2" bar. My concern is the drill hole is 1.4" leaving about .3" wall thickness over the 2" section on top and bottom. I wasn't sure if this would be weaker or stronger than the 3/4" shackle with thicker walls but less surface area. There is also three sizes of shackles between this. 7/8,1", and 1 1/8th. I'll try to post a pic to illustrate. BAIRSTOW.COM has a shackle chart of crosby G2130 models with dimensions. Any help appreciated.

 

[Kryptonight]

This is an example if the link works.

 

[desertfox]

Scroll down till you come to bolts withstanding shear loading, your situation is one of double shear however the insert will be subjected to the full load of whatever your winching. My only concern though is that I would of thought there would be some kind of specification or code laying down material requirements etc. for such equipment lifting equipment, I not sure where you stand legally if your insert fails during use.

http://www.roymech.co.uk/Useful_Tables/Screws/Bolted_Joint.html

 

[Kryptonight]

I have no liability as far as general public. Just my own use on my own truck. Not for any job related activities. Yes the double shear looks accurate. The load being applied is dynamic and variable depending on conditions of recovery, if vehicle is stuck in mud or pulling a fixed object like a tree trunk. I would def try to pre tensions the straps and not hit the shackle with any significant yanking motion. Come along possibly. The worst case and senario I'd like to avoid would be the shackle ripping itself out of the insert or breaking itself while being pulled. That could then launch toward whatever is pulling against it. A tree stump not a big deal but another vehicle could be bad.

There has got to be a minimal material size to anchor a shackle to. With bolt hole size to stock dimensions at some ratio. I want to avoid the shackle tearing out so I'm trying to use the largest shackle I can apply to this 2x2 insert. But looking closer to the 1.25 shackle I noticed the eyes are about 3 inches which I'm guessing would cause some unsupported area under the top and bottom edges of the nut and bolt head. I realize the nut and bolt head are fully supported by the eyes of the shackle but the eye would be in less than full contact with the 2x2 square.
So further looking I'm guessing the 7/8 size shackle with 1" hole through 2x2 stock and 2" eyes are Prob ideally balanced. Thanks for reply.

 

[MintJulep]

Using a shackle with a bolt or pin larger than the lynch pin that holds the insert into your hitch receiver is sort of a waste.

 

[Kryptonight]

It can't hold a side load as well as the hitch pin 5/8" and thick walled reciever upgrade is In the works. So regardless of the hitch pin there has to still be a ideal ratio of bolt hole size to material.

 

[ztengguy]

Those are usually 4:1 safety factor. more than likely you will slide your vehicle first.

 

[hydtools]

Ideal ratio would be tensile area strength equal to shear area strength.

Ted

 

[chicopee]

I believe that Crosby shackles have a factor of safety of five, however, their equipment is for hoisting and rigging applications on construction job sites and manufacturing/fabricating sectors. In you case, do you need a factor of safety of five?

 

[racookpe1978]

OK, now let me back up and point out that there is a lot to said for the idea of "failing slowly and gracefully" ...

So, this is a private individual working in unsafe and unconventional environs away from firm pavement, right-side-up pavements and good ground trying to pull - in an emergency situation, or at minimum unplanned situation - an unknown load out of an unknown ditch from unknown terrain over unknown slopes and vegetation.

Why not "un-design" the shackle shaft so it is the "first" to fail, but it fails by bending and yielding visibly a long time before it breaks suddenly. And before anything else breaks suddenly!

So, if the car or pickup is too heavy or the wheels trapped in the mud by a log, the strain begins everywhere - as you would expect! - but then the shackle bends and distorts. He stops pulling, and the rest of the gear (truck hitch, wire, welds, links, rope, etc) are not broken.