There are two types of axle bolts, with each performing nearly the same job. Axle bolts are strong bolts made of hardened steel that are used to connect the drive axle of a vehicle to a wheel hub or to connect axle half shafts together. Commonly consisting of the axle bolts and locking washers, the bolts are often installed using liquid thread-locking compound as well as a lock washer.
On a full-floating type axle as is typical on heavy-duty pickup trucks and other heavy trucks, the axle bolts are used to secure the axle to the wheel hub. Commonly consisting of eight axle bolts, the bolts are placed through the axle flange and threaded into the corresponding bolt holes in the wheel hub. In order to remove a full-floating axle, the bolts are removed from the axle flange and set aside. The axle shaft is then pulled from the wheel hub and removed from the axle housing. In some high-performance applications, the bolts are used to secure a drive flange to the wheel hub and a straight axle with a spline at each end is held in place between the differential and the drive flange.
In vehicles with independent suspension, axle bolts are commonly used to connect the outer half-shaft assembly to a yoke or drive flange protruding from the differential. Typically used in sets of four or six bolts, the axle shaft is held firmly in place and connected to the center section of the drive axle by the high-strength bolts. In cases of four-wheel drive vehicles, adding a suspension lift kit involves removing the bolts and separating the axles at the flange. An aluminum or steel spacer is usually added between the drive flange and the axle shaft, requiring longer bolts to compensate for the thickness of the spacer.
Adding a spacer negates the need to add longer axles when installing a vehicle lift kit. In some extreme lift kits, the spacers are designed in such a manner that two complete sets of axle bolts are used to install each side's spacer block into the axle. Instead of a single bolt running through the axle, the spacer and into the drive flange, a short bolt is used to connect the spacer to the drive flange. Another short bolt is used to attach the axle to the spacer block. Using two bolts per side is often stronger than using one very long bolt per side.