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Old 11-24-2015, 09:19 PM   #11
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A table for Bolt Torque Specifications (dry) from our friends in Pender, NE
Torque in Foot-Pounds for Inch Bolts
Bolt Size then Grade 5 then Grade 8
1/4”
10
14

5/16”
19
29

3/8”
33
47

7/16”
54
78

1/2”
78
119

5/8”
154
230

3/4”
257
380

Manufacturer torque specs may differ as they are application specific.
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Old 11-27-2015, 08:55 AM   #12
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Thanks Duck. These torque specs are max torque based on the strength of the material. Is that correct? Similar to the max pressure you might see posted on the side of a tire?


A manufacturer might specify less depending on what the bolt was being used for but should not specify a higher rating than what is shown on the chart?


So what effect does the length of the bolt and number of threads have on the torque specs?


I'm just sorting this out in my head and my fingers happen to be typing at the same time. A defect in my DNA causes this.


Roll
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Old 11-27-2015, 03:36 PM   #13
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Quote:
Originally Posted by Roll View Post
The replacements are grade 5 though grade 8 would naturally be better.

Wow 110 ft-lbs is a lot for a half inch bolt. The Dealer looked up the torque for me and said it was 75 ft-lbs.

Where did you get your info, maybe the Dealer was wrong.

Roll
Roll,
Here is the source for the 110 ft-lbs that I used: https://www.fastenal.com/en/83/torque-calculator
Their calculator actually indicates 106.4 ft-lbs for a Grade 8 1/2 inch coarse thread dry. I rounded up to 110. This is within the accuracy of my torque wrench. Also, the flange bolts + flange nuts might take a little more torque to reach the recommended bolt tension.
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Old 11-27-2015, 07:27 PM   #14
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Interesting discussion but without getting too far into the weeds and off topic, basically the application has everything to do with bolt size and torque specs. Fine threads do have slightly higher tensil strength because of the wider cross section but they are easy to crossthread and are usually only used in precision applications in the sizes we are talking about. The chart I posted is from BlueOx. Their products are similiar to the application in question so it is a reasonable comparitive. The length is not considered as the tensil strength is the same.

Edit: BTW, LLVanB's 110 ft lb number is a good # and easy to set on the T-wrench.
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Old 11-29-2015, 09:55 AM   #15
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Dup entry, sorry....
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Old 11-29-2015, 09:56 AM   #16
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Quote:
Originally Posted by Duckogram View Post
Interesting discussion but without getting too far into the weeds and off topic, basically the application has everything to do with bolt size and torque specs. Fine threads do have slightly higher tensil strength because of the wider cross section but they are easy to crossthread and are usually only used in precision applications in the sizes we are talking about. The chart I posted is from BlueOx. Their products are similiar to the application in question so it is a reasonable comparitive. The length is not considered as the tensil strength is the same.

Edit: BTW, LLVanB's 110 ft lb number is a good # and easy to set on the T-wrench.
I'm most interested on your post because you said you got the infor from BluOx. I replaced the bolts and plastic washers in my towbar last year. I got the replacement "kit" from BluOx but when I asked about torque specs for the bolts in the tow bar they told me they don't set torque specs for it.

I found that almost unbelievable. I pressed it but they didn't budge and wouldn't provide any specific torque recommendations.

Anyone else run into this?

Gary and just to be clear, I am always interested in your posts Duck.
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Old 11-29-2015, 10:08 AM   #17
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Where is the threshold of fine and coarse when it comes to bolts? When holding a bolt in your hand and looking at it, how do you decide whether it has fine threads or coarse threads?

Bruce
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Old 11-29-2015, 11:32 AM   #18
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Lug nuts are course. Not a lot of threads. Fine threads would be something screwing into a soft material, Plastic, aluminum. Many lose together threads. Go to a hardware store and a clerk to show you what they look like!
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Old 11-29-2015, 11:43 AM   #19
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Quote:
Originally Posted by A32Deuce View Post
Lug nuts are course. Not a lot of threads. Fine threads would be something screwing into a soft material, Plastic, aluminum. Many lose together threads. Go to a hardware store and a clerk to show you what they look like!
I understand this much, but what I am more interested in is at what TPI a bolt goes from being a coarse thread to a fine thread. It seems like there must be a gray area and the difference is mainly left to one's opinion.

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Old 11-29-2015, 12:10 PM   #20
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Quote:
Originally Posted by Roll View Post
I'm most interested on your post because you said you got the infor from BluOx. I replaced the bolts and plastic washers in my towbar last year. I got the replacement "kit" from BluOx but when I asked about torque specs for the bolts in the tow bar they told me they don't set torque specs for it.

I found that almost unbelievable. I pressed it but they didn't budge and wouldn't provide any specific torque recommendations.

Anyone else run into this?

Gary and just to be clear, I am always interested in your posts Duck.
I'm not surprised as the answer you received is correct based on how you asked the question. I did a test fitment for a blueox bedsaver on the Ford/Reese Elite 25k hitch after Ford offered them as OEM. The instructions for the basic unit did not have specific specs so I used their basic table. The patient lived.
Next was the Blue Ox Tiger Track for my F53. Again, there are no torque specs for each bolt however, they did publish the generic specs for their applications on the instruction sheet. Here is a link to that reference.
http://blueox.com/wp-content/uploads...01/TT24002.pdf

In order to set specific torque specs you would have to test each bolt on the specific application. I think there is a machine for that but I will venture a guess that using the bolt manufacturers specs lessen corporate liability.
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