When sourcing truck axles, the most critical factor is the Load Capacity (GAWR - Gross Axle Weight Rating), which must align with the vehicle's intended use. You should verify the housing material, typically high-strength pressed steel or cast iron, to ensure structural integrity. Additionally, pay close attention to the gear ratio for drive axles, as this directly impacts fuel efficiency and torque performance. For heavy-duty applications, ensure the axle features induction-hardened spindles and precision-ground bearings to minimize friction and heat buildup.