Why is the pin a structural part?
The pin or bolt carries the structural load through the joint, and it may also act as a journal, the surface the ball turns on. So it must be strong, wear little, have low friction and resist corrosion. A sensible pin is heat treated to the required strength, then ground and polished to a finish of 8 µin Ra (about 0.2 µm) or better.
Think of the pin as two jobs at once. It carries the load across the joint, and it is the shaft the ball rotates on. A pin that is strong enough but rough will wear the ball bore, and a smooth pin that is soft will deform under the load. Both failures look like "the rod end has play" from the outside, which is why the pin is the first thing to inspect.
What fit should the pin have in the ball bore?
A typical fit between the pin and the bearing bore runs from line-to-line to 0.001 inch loose, about 0.025 mm (the range NHBB gives for its own bearings). "Line-to-line" means there is no interference, and "loose" means a small free clearance. Other makers differ, so take the fit from the rod end's maker rather than from this article (K03-Q1-14).
Single shear or double shear?
Double shear is the better arrangement, and it is often available. When the rod end sits between two supports, a clevis or a fork, the pin passes through two cross-sections, and the load is shared between them. A clevis is a U-shaped bracket that supports the eye on both sides, which is what sets up double shear.
The shear stress in double shear is 2F ÷ (π × d²), where F is the force and d the pin diameter. A rod end bolted against a single bracket puts the pin in single shear. Now there is one cross-section, so the same force gives twice the stress: 4F ÷ (π × d²). Take a 10 kN load on a 12 mm pin. In double shear the stress is 44 MPa. In single shear it is 88 MPa.
Single shear also brings a second problem. The load is usually off to one side of the bracket, so the pin is bent as well as sheared. That is why a rod end in single shear needs a bigger pin, or a second support, before it needs a stronger material. Check the pin for the arrangement you actually have (K05-Q1-05).
How firmly should the inner ring be clamped?
Firmly, but not so hard that it binds. In most installations the bolt is preloaded with the nut to clamp the ball, so the ball turns on the race and not on the bolt. Excessive force expands the ball and binds it in the race.
The reasoning is simple. If the inner ring is loose, the ball can turn on the bore instead of the race. When the ball is not clamped, motion takes place on the bore, and then the bolt, the bore or both must have surfaces made for that motion. Clamping the ball faces keeps the motion on the race, where the bearing is designed to take it. Too much clamp force does the opposite: it expands the ball and closes the internal clearance, so the joint binds. The right clamp sits between those two outcomes, and the maker's instruction sets it. Use spacers or washers that clamp the inner ring faces without touching the housing (Q1-06).
What do spacers do?
A spacer between the ball and the bracket centres the rod end so it runs straight. A tapered, high-misalignment form also lets the housing tilt further before it meets the bracket (K11-Q1-01).
A clevis, a bolt head, a washer or a spacer can restrict movement before the rod end reaches its catalogue limit, and deflection under load can reduce the clearance further. So check the clearance through the whole cycle, not at rest: between the housing and the bracket, and around the bolts, washers and spacers (K03-Q1-09).
What about the fit in the housing?
When a bearing is pressed into its own housing, a heavy interference fit is not recommended, because it reduces the internal clearance the bearing needs. If the fit must be tight, assemble it with a temperature difference rather than by forcing it (K02-Q1-10).
How do you avoid side loads at installation?
A side load starts at installation. If the two brackets are not parallel, or the rod end is pulled into place by its eye, the pin is bent before the machine has run. Check that the mounting faces are parallel and that the pin enters both brackets straight, and tighten only the way the design intends. A bent pin should be replaced, not straightened.
How does single-shear mounting change the pin check on a chassis bracket?
Chassis brackets are often a single tab welded to a tube or a plate, so single-shear mounting is common, and the load arrives as hard peaks that, on a locating link, also reverse. Take the illustrative 16.6 kN peak from the sizing example in Q1-02 on a 12 mm pin. In double shear the shear stress is 2 × 16 554 ÷ (π × 12²) = 73 MPa; in single shear it is 146 MPa, before the bending that the offset adds. If the layout allows it, add the second support, a tab on the other side or a clevis-style bracket, so the pin goes back to double shear.
Spacers matter more because the travel is long. The housing has to clear the bracket at full droop and full compression, and the stack of spacers and washers sets the clearance. Check it with the suspension moved to both ends, not at ride height (Q1-06, K11-Q1-01). Also keep the bolt shank, not its thread, across the shear plane where the layout allows it, and replace a bolt that has seen a hard impact rather than reuse it.
The bolt, the bracket and the weld are safety parts, and their sizes and torque come from the vehicle's designer. For the double-shear case, see the bolt shear capacity calculator; the spacer range is on the spacers page.