HotRodYJ
01-04-2007, 04:03 PM
I've often wondered is it better to use a 3/4" x 3/4" rod end or a 3/4" x 5/8" rod end. For those who don't know, this size means 3/4" shank size and either a 3/4" or 5/8" hole or bolt size. My opinion up till know is I don't want to shear the smaller 5/8" bolt so I go overboard with the 3/4" bolt option for higher shear strength. The down side is a 3/4" x 5/8" rod end will have a higher operating angle than a 3/4" x 3/4", and the 3/4 x 5/8 rod end has a 30% greater static strength. I dug around a little and came up with shear strengths for grade 8 bolts to help in the comparison based on the chart found in this link...
http://www.rockcrawler.com/techreports/fasteners/index.asp
Basically...
A grade 8, 3/4" bolt has a shear strength of 40,200 lbs
A QA1 Chromoly rod end (3/4 x 3/4) has a static load rating of about 28,800
A grade 8, 5/8" bolt has a shear strength of 27,920 lbs
A QA1 chromoly rod end (3/4 x 5/8 ) has a static load rating of about 40,400 lbs.
The end result is very close so it's almost a call on what would you rather break the rod end or the bolt? My concluion is it depends on what the end is used for and if it is used in single shear as with steering components, or double shear as in suspension links? Looks to me like your much better off to use the larger 3/4" bolt in a single shear application and use the 5/8" bolt for double shear applications. In double shear use, the 3/4 x 5/8 rod end is far superior and stronger because you get the high strength on the rod end itself and the load on the bolt is cut in half since there are two shear points, so a 5/8" bolt in double shear could handle almost 56,000 lbs of force at the bolt holes (27,920 x 2), so the 40,400 rating on the rod end becomes the weakest link.
I also keep in mind that a bolt in single shear application such as steering links also have a bending force, so it's not simply the static and shear ratings alone, but these forces are compounded by bending forces. I believe most single shear applications are far more likely to fail due to fatigue and stress cracking from teh bending forces than failure by shear loading or static loading alone. For this reason, I believe the 3/4 bolt for steering may be a safer option, unless you can do a double shear monting which is always the best method, but not always feasible.
Thought this might help someone else. It helped to clear up some questions I had.
http://www.rockcrawler.com/techreports/fasteners/index.asp
Basically...
A grade 8, 3/4" bolt has a shear strength of 40,200 lbs
A QA1 Chromoly rod end (3/4 x 3/4) has a static load rating of about 28,800
A grade 8, 5/8" bolt has a shear strength of 27,920 lbs
A QA1 chromoly rod end (3/4 x 5/8 ) has a static load rating of about 40,400 lbs.
The end result is very close so it's almost a call on what would you rather break the rod end or the bolt? My concluion is it depends on what the end is used for and if it is used in single shear as with steering components, or double shear as in suspension links? Looks to me like your much better off to use the larger 3/4" bolt in a single shear application and use the 5/8" bolt for double shear applications. In double shear use, the 3/4 x 5/8 rod end is far superior and stronger because you get the high strength on the rod end itself and the load on the bolt is cut in half since there are two shear points, so a 5/8" bolt in double shear could handle almost 56,000 lbs of force at the bolt holes (27,920 x 2), so the 40,400 rating on the rod end becomes the weakest link.
I also keep in mind that a bolt in single shear application such as steering links also have a bending force, so it's not simply the static and shear ratings alone, but these forces are compounded by bending forces. I believe most single shear applications are far more likely to fail due to fatigue and stress cracking from teh bending forces than failure by shear loading or static loading alone. For this reason, I believe the 3/4 bolt for steering may be a safer option, unless you can do a double shear monting which is always the best method, but not always feasible.
Thought this might help someone else. It helped to clear up some questions I had.