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An axle flange is the part of an axle that has the wheel studs coming through it in order to mount a wheel to the axle. The flat, circular axle flange typically rests inside of the wheel drum or disk assembly, directly opposite the wheel bearing. Used primarily in rear-wheel drive vehicles, the axle is frequently removed from the axle housing by removing four retaining bolts which are accessed through a large hole in the flange. While it is typical for the wheel studs to be attached to the axle through pre-drilled bolt circle holes, it is not uncommon for a flange to be drilled with two different bolt patterns.
The axle flange is responsible for three functions on the average vehicle. First and foremost, the axle flange houses the wheel studs that the lug nuts are threaded onto in order to secure the vehicle's wheel assembly. The flange also provides an attachment point for the brake drum or disk to slow the wheel. The flange also has a center high spot machined into its face that centers the wheel once it is slid onto the wheel studs. Not all axles incorporate a flange, as some front-wheel drive vehicles use an axle that is splined to receive a hub assembly in place of the flange.
Some vehicles utilize a splined axle flange that is secured to the axle shaft with a large castellated nut and cotter pin. This type of axle is not as strong as the one-piece axle design, and excessive horsepower can easily rip the axle through the splined connection. Once this occurs, the axle will simply spin inside of the flange and will not propel the vehicle forward or backward. Occasionally, this can be remedied by welding the flange to the axle, however, this is a short-term fix and the axle should be replaced at the earliest opportunity.
Some aftermarket manufacturers make and market a one-piece axle to replace the splined axle flange with a stronger unit capable of withstanding more power. These are popular with many off-roaders and drag-racing teams. The Ford Motor Company makes one of the strongest axles. Ford's axle is being used in vehicles ranging from pickup trucks to nitro-methane-burning dragsters. This Ford flange is frequently re-drilled to allow other manufacturers' wheel bolt pattern circles to fit onto the Ford axle.