Both the upper and lower headset bearings, two bearings included in sale.

For all Bird bikes using the Bird ZSI Headset Bearing Kit

Upper Bearing - MH-P03K

Lower Bearing - MH-P25K

• GCR15 High Carbon Chromium Bearings: Chromium offers a corrosion resistance to the bearing, allowing you to get more use out on the trails and less time in the workshop changing bearings again due to rust and seizing.
  
• Buna NitrileRust Resistance Seals: Prevents moisture getting inside the bearing.
• Packed With Lithium Grease : Keeps the bearings running smooth and protected from the elements, grease also contains rust inhibitors and anti oxidants for further performance gains.