The steering knuckle provides an attachment point for the tie rod to the wheel.
The steering knuckle also provides an attachment point for the upper and lower
ball joints in conventional A frame suspension system. With Macpherson strut
systems,the steering knuckle anchors the lower end of the strut and the lower
ball joint.
The spindle of a rear wheel drive vehicle is supported and attached by the steering
knuckle. With a front wheel drive vehicle, the front hub and bearing assembly is
attached to the steering knuckle. Disc brake systems also use the steering knuckle
as a mount for the brake caliper. The components attached to the steering knuckle
will usually wear out before the steering knuckle itself. In fact, most of the damage
to a steering knuckle will occur from collision damage.

Avaialbe from your OEM No.