Every axle has a specific stock spline size, or count, and is determined by counting the physical splines on the axle itself. It is important to know the spline count for your vehicle before purchasing new axles to prevent axle failure. Many axle housings have different spline counts or sizes depending on the year of manufacture and vehicle application, making identification only by axle housing or vehicle make and model unreliable.
The spline count on the axle has to match up to the spline count in the differential carrier for the axle to function properly and provide the appropriate amount of torque. Generally speaking, a larger number of axle splines yields a stronger axle than a lower number. Other than counting splines on the axle, a dealership may be able to identify spline count by VIN and for a Dana Spicer axle housing, entering the bill of materials to dana.com will provide a spline count.
For daily driving, the stock axle spline count will always be sufficient. For more aggressive driving like rockcrawling, modbogging or drag racing, upgrading the spline count on the axles can provide more stability and power. Companies such as Mark Williams Enterprises and Yukong Gear and Axle manufacture axle spline upgrade options for many applications.