Let's face it, Bearings, spacers, and axles can be unnecessarily complicated so let's try and make this easy. These inline axles have an outer diameter of 6mm. Most bearings have in inner diameter of 8mm. These spacers make standard 8mm bearings compatible with 6mm axles. Purchasing the correct length axle is the key factor and we have found that both 30mm and 33mm axles are somewhat interchangeable and will fit on most skates while 36mm are generally large and do not fit on many skates. It is very important for you to measure your current axle’s length to ensure a proper fit. Includes 8 Axles (nuts and bolts) and 8 Spacers.