Specialized Zero Stack Headset Cups Description: These Specialized Zero Stack Headset Cups are a custom sized bearing cup intended for DSW Alloy Road and Gravel bikes. This set is a factory replacement for damaged or missing headset cups. Includes (one of each): Zero stack upper headset cup for 41.8mm (outside diameter) upper bearing Zero stack lower headset cup for 49.5mm (outside diameter) lower bearing Bearings, compression rings, and other headset parts sold separately Specifications: Upper Outside Diameter: 44.5mm Lower Outside Diameter: 52.5mm