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Old 12-19-2008, 12:27 PM   #15
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I think in this instance, the ball is the least likely item of the hitch system to fail! The math suggests the ball is much stronger than the rating and much stronger than is needed. A 1" shank has a cross sectional area of .785 sq. inches. Most common structural steel has a modulus of elasticity of 36ksi or 36,000 pounds per square inch, therefore:
.785 x 36,000= 28,260 pounds or 2.8 times the rating for a 10,000 lb. rated ball with a 1" shank. Keep in mind, this is with basic common structural steel. . . (snip)
Except in this instance, Bob, it would fail the SAE standard, which requires 3X the rating, or 30,000lbs.

And it still doesn't answer my question: what is the rating of the ballmount it's attached to?
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Old 12-19-2008, 12:37 PM   #16
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Now you have me curious again. Where can I find this 3X SAE standard so I can read more! Most structural steel has a safety factor of between 1.4 and 1.7 depending on where it is used in an assembly.

Aside from that, 50 ksi (high strength structural) steel would easily meet any 3X SAE standard with a strength of 39,250 pounds or a 3.9 safety factory. Grade 8 steel would have a modulus of elasticity of between 120,000 and 150,000 pounds per square inch or in this case, a safety factor of at least 9.4 . You get the idea.
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Old 12-19-2008, 12:45 PM   #17
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Bob,

I agree you can find hitch balls with 1" shanks that meet the SAE standards. Whether they are high strength steel or forged, I don't know. Iknow they're out there.

But it does explain why the standard, made out of 36k steel, hitch balls that you find in the bargain bin at Menards are only rated for 6000#.

It also backs up my reasoning for having a rating on the hitch head or drawbar. If you can put a 10,000# rated ball with a 1" shank on a cheap Class III drawbar, doesn't mean the whole shebang is now worth 10,000#.
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Old 12-19-2008, 12:47 PM   #18
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. . . and the SAE standard is J684, section 6.5.2, and table 2.
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Old 12-19-2008, 06:48 PM   #19
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Yep, there it is, SAE Standard J684 for Trailer Hitches, Couplings, and Safety chains, In Table 2 under Class 4 hitches (and only under Class 4 hitches) it does have a requirement that hitch balls be able to withstand horizontal thrusts equal to the weight of the trailer x 3. For us, that would mean the rating of the hitch assembly. For Class 4 hitches, common 36ksi steel won't work for balls with a 1" shank but high strength 50 ksi steel will.
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Old 12-19-2008, 07:35 PM   #20
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Isn't this a set up for a punch line?


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Old 12-19-2008, 07:40 PM   #21
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Bob, the 3 x weight rating applies to the other classes as well.

Class I 2000# x 3 = 6000#
Class II 3500# x 3 = 10500#
Class III 5000# x 3 = 15000#
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Old 12-20-2008, 12:07 AM   #22
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Yes, you are correct. The math confirms the numbers given in Table 2 translate to a safety factor of 3x for Class I, Class II, and Class III hitches as well. Good catch!
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