Rod Ends: Threaded Clevis (PR) and Weld-On (S) Cylinder Mountings

A hydraulic cylinder is never bolted rigidly to its load. As the cylinder works, the axis of the load shifts, the machine frame flexes, and the line between the rod end and the rear mounting is thrown out. In a rigid connection that misalignment goes straight into the rod as a side load — and the rod is then carrying a force the seal and the bearing were never meant to take.

The consequence is well known in the field: the seal begins to leak on one side, the rod bends slightly over time, the plating scores. The replacement seal leaks again a few months later, because the seal was never the cause. A rod end is used precisely to release that misalignment — to let the cylinder swing with the load.

There are two types. The threaded clevis type (PR series) screws onto the thread at the end of the rod; the load pin passes through the jaw. The weld-on type (S series) is welded to the machine frame and comes in two sub-types: C with a round body, N with a rectangular one. The choice depends on the shape of the surface being welded to and how tight the space is.

The size figure is the diameter of the pin bore: 20 mm on a PR20, 50 mm on an S 50 N. It is selected from the pin that carries the load, not from the cylinder's rod diameter — confusing the two is a frequent mistake. On the threaded type the thread size at the rod end must match as well.

Once fitted, greasing the pin should not be neglected; a rod end run dry quickly wears oval and develops play. As the play grows, the cylinder knocks on every reversal — that noise is the signal that the rod end is due for replacement. For the cylinder itself see «Hydraulic Cylinders», and for the seal group see «Hydraulic Seals, Nutrings and Wipers».