The axleshaft, brake backing plate, and outer bearing are held in place with four bolts. Many Toyota axles use a solid-state tone ring for each wheel speed sensor and the Tundra is no different. These rings look like an axle seal, but are actually embedded with magnets that allow the speed sensor to know how fast the wheel is turning and which direction, and are helpful for both antilock braking systems and traction control. Also note how large the axleshaft is at the bearing where it supports the weight of the truck. From there it gradually necks down to the splines.