What are the strongest 5/8" hitch pins for recovery use?

[DaveInDenver]

Great points but I'll say from experience that Grade 8 is way more prone to brittle breakage than Grade 5. That's why Grade 5 is called out in many applications and specify not to use 8. As somebody who has replaced grade 8 with grade 5 bolts because of breakage and lack of clamping stretch, lack of reusability in bolt applications I can attest to that. Cost savings of grade 5 aren't that significant, so why don't we just use Grade 8 everywhere? Again depends on application and engineering call outs.

I know nothing really and you're probably right, I'm sure in this application the welds will fail before the pin. But I'll stand by my preference for bending rather than breaking in winching.

This is not true. A grade 8 bolt is always higher strength than a grade 5.

While you are right that heat treating to achieve grade 8 does cause the plastic region of the bolt to decrease. That only means that the transition region from recoverable bending (elastic, meaning it returns to it's original shape) to permanent deformation (elongation) to ultimate is smaller.

However the flip side is the point where a grade 8 starts to elongate is higher than the yield (break) point of a grade 5.



Putting numbers to it. Say you have a 5/8" bolt and for the sake of argument you only look at the unthreaded shank so that it's actually 5/8" diameter.

The sectional area is:



The specs for bolts are generally by ASTM A354 or SAE J429.



5/8" SAE Grade 5:
Proof of 85 ksi * 0.31 sq-in = 26,350 lbf
Yield of 92 ksi * 0.31 = 28,520 lbf
Ultimate of 120 ksi * 0.31 = 37,200 lbf

5/8" SAE Grade 8:
Proof of 120 ksi * 0.31 sq-in = 37,200 lbf
Yield of 130 ksi * 0.31 = 40,300 lbf
Ultimate of 150 ksi * 0.31 = 46,500 lbf

BTW, as it happens a Grade 8 5/8" bolt has very nearly the same ultimate strength as a standard 4.75 ton bow shackle. That rigging is dictated by the ASME B30.26 standard to have a minimum of 5:1 design margin.

So a WLL shackle at 4.75 ton WLL will break no lower than 5 x 4.75 tons = 23.75 t = 47,500 lbf.

Although sticking to the proper WLL of 9,500 lbf on this shackle is exceeded by either Grade 5 or Grade 8 so there's no concern to using either as a hitch pin. Proof load per ASME B30.26 is 2:1, so a 4.75t shackle will handle 19,000 lbf without damage and even this is still lower than proof on both bolt types.

The reason various SAE grades exist is mainly cost. If you don't need Grade 8 and it costs a nickel more to the OEM per bolt they'll use the lowest spec that meets the need and put the difference to profit using millions of them.

 

[J!m]

I find the bow rig interesting.

If it’s a straight pull, two straps are fine, but unnecessary. Use one (assuming it’s long enough) and then a second, not under tension, from shackle to one secure point on the vehicle. You get the flexibility of a sliding bow with the safety of a redundant (but non-interfering) safety strap.

Rigging can take time but should not be rushed.

One should also be aware of the derating that comes with any rigging other than a straight line pull. The bow (basket might yield more derating results) is not rated as high as the strap used to make the bow. I think it’s 10-20% derating but that’s off the top of my head…

 

[Sid Post]

Clevis D-Shackle - 3/4" with 7/8" Pin - 18,000 lb - 88999

This 3/4” [20 mm] shackle has 7/8” [22 mm] pin diameter, for 18,000 lb (8164 kg) capacity winches and under.

www.warn.com

Is this really an 18K pound shackle? Or is this a non-WLL rating?

 

[Metcalf]

Clevis D-Shackle - 3/4" with 7/8" Pin - 18,000 lb - 88999

This 3/4” [20 mm] shackle has 7/8” [22 mm] pin diameter, for 18,000 lb (8164 kg) capacity winches and under.

www.warn.com

Is this really an 18K pound shackle? Or is this a non-WLL rating?

Something similar industry standard, like a Crosby G-209 3/4" shackle, is going to be 'rated' for a WLL of 4.75t ( 10.5k lbs) or so. That is going to be at a 6:1 FoS however to be compatible with a lot of overhead lifting standards.

You are going to have a very hard time breaking any 3/4" hard shackle. I do have my reservations and doubts about whatever that 2-3lb steel potential missile is attached to, that is why I have made a hard push toward synthetic rigging whenever practical. There are a LOT of existing recovery points on vehicles built with sharp hard edged holes that will work better with steel shackles however. It is always worth the time for a 2nd look at the supporting structure behind the recovery point to me. I will also run an independent leg bridle whenever practical to help spread out the load if there is any doubt.

 

[colodak]

Learned this recently, a "hitch pin" as supplied for a receiver hitch is designed for towing, not for recovery, different stresses, while a towing use is a more constant stress, and a recovery is a sudden, occasional stress, they are different. I was delivering to a farmer, got the semi stuck, not super stuck, but just enough. The farmer went and got his F450, backed up to me, slipped in his receiver tow hook, it looked something home brewed, 2" dia square tube with a 7/8" shackle, using a synthetic tow strap rated to 50K (specifically designed for farm use), hooked it to my tow hook on the semi and gave it a couple good yanks, first yank did nothing, second yank I started to move forward, third yank the "hitch pin" sheared in half, the receiver hook came flying back at my truck with enough force to put a large bent in my bumper and crack the grill. The medium duty wrecker that came to yank me out had a recovery shackle assembly with a 5/8" pin, that was noticeably heavier by feel that a regular hitch pin. I'm not sure who made that unit, but from looking at it, it had obviously seen some recovery work from the way it was marred up, the tow company owner said the pin was stronger than a regular tow pin and was specifically designed for recovery work.

 

[Metcalf]

Learned this recently, a "hitch pin" as supplied for a receiver hitch is designed for towing, not for recovery, different stresses, while a towing use is a more constant stress, and a recovery is a sudden, occasional stress, they are different. I was delivering to a farmer, got the semi stuck, not super stuck, but just enough. The farmer went and got his F450, backed up to me, slipped in his receiver tow hook, it looked something home brewed, 2" dia square tube with a 7/8" shackle, using a synthetic tow strap rated to 50K (specifically designed for farm use), hooked it to my tow hook on the semi and gave it a couple good yanks, first yank did nothing, second yank I started to move forward, third yank the "hitch pin" sheared in half, the receiver hook came flying back at my truck with enough force to put a large bent in my bumper and crack the grill. The medium duty wrecker that came to yank me out had a recovery shackle assembly with a 5/8" pin, that was noticeably heavier by feel that a regular hitch pin. I'm not sure who made that unit, but from looking at it, it had obviously seen some recovery work from the way it was marred up, the tow company owner said the pin was stronger than a regular tow pin and was specifically designed for recovery work.

A few notes on this....

-Using a section of 2" square tube to base a recovery device on is a miss. The pin needs to be supported across its entire span to achieve it's maximum strength.

-Pin's definitely come in different strengths and there isn't a lot of 'rating' on many units. I will say that even a decent commercial quality unit will fail north of 30k and a very high quality unit will be approaching 60k. Most receiver assemblies are going to have a hard time getting to those numbers without plastic deformation in the cross tube ( common early sign of failure )

-Any pin regardless of strength, should be inspected often for wear and pre-failure indicators. Since they are running in a non tensioned system their entire life, they do wear over time.

- 'Tow Strap' is a bit of a red flag. It will be hit or miss if that strap was designed to be 'yanked' on. Only straps made from NYLON will have the elastic properties you want to be able to do a kinetic recovery. If the strap is Polyester, it will have much less stretch and impart MUCH more impulse load to the mounting hardware, especially if the strap has a very high weight rating.