Shear loads are applied in a manner that is literally trying to cut the material in half (think scissors) and is most often used in highly stressed areas. As a rule of thumb, shear loads are considered to be 60 percent of the material's tensile strength. For example, if a part has a tensile strength of 10,000 pounds, then the shear strength of the material would be 6,000 pounds.
Axial load refers to a heim joint and is the load applied along the bearing bore axis (where the bolt goes through) commonly seen when using the spherical part as a ball joint.
What size material should you use for a particular application? I can't tell you, it is too hard to say specifically what size material/part to use. After a quick call to my buddy, Jack at hm-engineering.com, we netted some spherical bearing (heim joint) information, and the rest of the info was found out on the webbernet. Let's take a look at some commonly used parts and material.
| In pounds… | Tensile strength | Shear |
| Grade 8-1/2-inch bolt | 21,000 | 12,600 |
| Grade 2-1/2-inch bolt | 10,500 | 6,300 |
| High grade 3/4-inch heim | 28,000 | not recommended for axial use |
| Low grade 3/4-inch heim | 14,300 | not recommended for axial use |
| High grade 3/8-inch heim | 9,550 | not recommended for axial use |
| 1-inch uni-ball | 104,000 | 19,300 (axial) |
| 7/8-inch uni-ball | 67,000 | 10,800 (axial) |
| 3/4-inch uni-ball | 53,000 | 8,000 (axial) |
| 1-1/2-inch x .250 DOM | 78,560 |
| 1-1/2-inch x .250 4130 | 88,380 |
| 1-1/2-inch x .120 DOM | 42,960 |
| 1-inch x .120-inch DOM | 27,200 |
I know... What about the right size material to use on my frame? The best I can say is to look at what the vehicle came with stock and think similar. If the frame was 2x5-inches x.120-inch C-channel, then it is reasonable to think that you could get away with 2x3-inch x.120-inch boxed tubing. The frame flexed from the factory, you can expect it to flex once you modify it. Trying to eliminate any frame flexing is impossible without a roll cage, just do your homework and keep stress risers to a minimum.
Overbuilding is safe, but where do you draw the line? A solid frame, 2-inch heim joints, a rearend from a trash truck?
-Max Fish