For any suspension link we recommend nothing less than a Grade 8 bolt (below right) and if you really want a strong bolt look into the F9-11 bolts from Foremost Threaded Products. F9-11 bolts are 20 percent stronger than most Grade 8 bolts and have a 180,000-psi minimum yield. And unlike many fasteners that you find at local hardware stores. Many suspension links have simple poly bushings with inner and outer steel sleeves. The outer sleeve is attached to the tube of the link in some way and the inner sleeve is where a bolt runs through the bushing and chassis or axle mounting tabs. Using bushings is good when you have links that need to keep from twisting. In the picture below, the upper bushing assembly is from Ballistic Fabrication and has a welded shank, while the lower bushings are from Poly Performance and can be assembled and welded by the suspension builder.
A 4-Link suspension allows free movement of the axles for greater articulation resulting in better traction on the trails or in the mud. A typical fully-linked suspension can have 4 links in front plus a track bar and 4 links in rear plus a rear track bar. A track bar keeps the axle centered while allowing the suspension to cycle. Another set up would be a double triangulated 4-link setup where a track-bar is not used, and this method can also be done in the front or rear of the vehicle.
Starting at the chassis mount location, the upper links are angle in toward the center of the axle while the lower links are closer together at the starting point on the frame and angle out slightly toward the ends of the axle. These opposing angles also keep the axle centered during articulation, and without the use of a track bar.
In The Past Two Decades Link-style suspensions have gone from a desert-race exclusive to something being built by knowledgeable fabricators. Link suspensions separate the jobs so that each component of the suspension can do its part exclusively and thus better. For example, the springs on a link suspension don’t locate the axle like a leaf-sprung suspension, so axle wrap is eliminated. Since the links move the axles in an arc that can follow the drive-shaft, U-joint bind is often reduced. Approach and departure angles can also be increased since the links do not stick out past the axle tubes