The bottom end bearing is a split-type bearing consisting of two semi-circular precision-insert shells housed within the "big end" of the connecting rod.

• Connecting Rod Big End: The larger, lower part of the rod that is split into two halves.
• Bearing Shells: Usually tri-metal (steel back, lead-bronze interlayer, and a thin white-metal or tin-aluminum overlay).
• Bearing Cap (Keep): The removable lower half that secures the assembly around the crankshaft journal.
• Connecting Rod Bolts: High-tensile bolts that clamp the cap to the rod.
• Oil Hole: A "rifle-bored" hole through the center of the connecting rod shank allows lubricating oil to flow from the big end up to the small end.

Serrations (teeth-like structures) are machined into the mating surfaces where the connecting rod meets the bearing cap. Their purposes include

• Positive Location: They ensure perfect alignment between the two halves, preventing any relative movement or "shuffling" during operation.
• Shear Load Resistance: They take the high transverse (shear) loads generated by the oscillating motion of the rod, preventing these forces from being transferred directly to the bolts.
• Fretting Prevention: By arresting relative movement, they reduce fretting corrosion on the mating faces.

Because these bolts are subjected to intense cyclic stress and load reversal, they incorporate several design features:

• Waisted Shank: The bolt diameter is reduced (waisted) between the head and the threads. This increases elasticity, allowing the bolt to stretch more effectively under load and better resist fatigue.
• Rolled Threads: Threads are formed by rolling rather than cutting to improve grain structure and increase fatigue strength.
• High Tensile Material: Usually made of high-grade alloy steel (e.g., chrome-molybdenum) to withstand extreme tensile loads.
• Stress-Reducing Fillets: Large, smooth radii are provided at the head-to-shank transition to minimize stress concentration