Replacing or upgrading skateboard bearings is straightforward because the industry relies on a single, highly standardized component. Skateboards, longboards, and scooters utilize a universal size known as the 608 bearing. This standardization ensures that nearly all wheels and trucks are compatible, allowing riders to easily swap parts.
The Standard Skateboard Bearing Size (The 608)
The 608 designation is part of a global system for identifying rolling element bearings. This code provides specific information about the bearing’s type and dimensions. The “6” indicates a single-row deep groove ball bearing, which is the most common type used in skateboarding to handle both radial and axial forces.
The final two digits, “08,” directly relate to the bearing’s bore, or inner diameter, which is 8 millimeters (mm). This 8mm opening is specifically engineered to slide perfectly onto the standard 8mm diameter axle found on nearly all skateboard trucks. The precise fit between the bearing bore and the axle is important for minimizing play and ensuring the wheel spins true.
The outer diameter (OD) of the 608 bearing measures 22 millimeters. This measurement dictates how the bearing seats within the polyurethane wheel itself, fitting snugly into the molded bearing pocket. The 22mm size ensures a secure press-fit, preventing the bearing from moving laterally or spinning within the wheel during use.
The third dimension is the width, or thickness, which is standardized at 7 millimeters. This 7mm width accommodates the space between the wheel’s bearing seats, allowing two bearings to fit within the wheel. The combination of these three measurements—8mm, 22mm, and 7mm—defines the universal 608 size.
Related Components and Fit (Axles, Spacers, and Exceptions)
The 8mm inner diameter of the 608 bearing is designed to interface directly with the 8mm axle of the skateboard truck. Before the wheel is placed on the axle, thin metal washers, commonly called speed rings, are positioned on the axle against the truck hanger. These small, precision-machined steel rings prevent the inner race of the bearing from rubbing against the rough surface of the truck hanger, which would otherwise create friction and slow the wheel.
Once the wheel is on the axle, a second speed ring is placed on the outside, just before the axle nut is tightened. This setup ensures that the bearing’s inner race is isolated and only contacts the smooth surfaces of the speed rings, allowing the outer race and the wheel to spin freely. The axle nut is tightened just enough to eliminate lateral wheel play without compressing the bearing and restricting its rotation.
Inside the wheel, between the two 608 bearings, a bearing spacer is typically installed. These spacers are usually small metal cylinders, often 10 millimeters wide, that sit on the axle. The spacer’s function is to maintain the precise parallel alignment of the two bearings and prevent the inner races from being compressed inward when the axle nut is tightened.
By filling the gap between the bearings, the spacer ensures that any force applied by tightening the axle nut is transferred through the spacer itself, rather than through the bearing’s internal components. This prevents side-loading, which is a major cause of bearing damage and premature failure. Using spacers helps distribute the load evenly across the bearing balls, promoting smoother and longer-lasting performance.
While the 608 is the overwhelming standard, a few specialized setups utilize smaller components. Some high-performance longboard or slalom racing trucks occasionally use micro-bearings, such as the 6900 series. These bearings feature a smaller 7mm bore and require specialized axles and wheels, but the 608 size remains the default for nearly all street, park, and cruising skateboards.