They are Aluminum Hex Wheel Hubs the T-Maxx and E-Maxx Truck Kits. Features: Blue anodized. Machined 6061 T-6 aluminum construction. Loaded in foam, on a bubble sealed header card. Includes: Four Hex Wheel Hubs Four 2.5 x 10mm Axle Pins Specs: Width: 13.0mm interior Diameter: 6.3mm