Dimensions and specifications OUTER DIAMETER: 0.8 inch20.5mm, INNER DIAMETER: 0.5 inch13mm, BALL DIAMETER: 316 inch. Please confirm the size before purchase ! Compatibility :This ball bearing is a replacement part for Stroller, bike parts replacement compatible with Baby Trend ExpeditionNavigator Stroller, bike parts replacement, suitable for bicycle front wheel axle, such as: mountain bike, kids bicycle, lowrider bike, children s bike, stretch bicycles. Note: 1. Apply some lubricant oil before installation 2. In order to make this replacement works longer, we pre-applied some lubricant oil in the package. 3.Please allow 0-1mm discrepancy due to manual measurement. Package includes: 2 x Bicycle Ball Bearings