The ZERO 40 x 51.9 x 8mm 45/45 Headset Bearing is a replacement cartridge bearing for compatible bicycle headset systems. It uses a 40mm inner diameter, 51.9mm outer diameter, 8mm height and 45°/45° contact angle, making it suitable for headset applications requiring the Ritchey-fit/ACB519H8 specification. South African bearing listings identify the equivalent as ACB519H8 / Ritchey Fit.
Key Features
40mm internal diameter
51.9mm external diameter
8mm bearing height
45°/45° contact angle
Angular-contact cartridge bearing
Designed for compatible bicycle headset assemblies
Suitable as a replacement for worn or damaged headset bearings
Equivalent to the commonly referenced ACB519H8 / Ritchey-fit specification
Specifications
Specification
Details
Brand
ZERO
Product Type
Headset Bearing
Inner Diameter
40mm
Outer Diameter
51.9mm
Height
8mm
Contact Angle
45° / 45°
Bearing Type
Angular Contact Cartridge
Common Equivalent
ACB519H8 / Ritchey Fit
Application
Bicycle Headsets
Compatibility
This bearing specification is used in a range of bicycle headset systems. The 40 x 51.9 x 8mm 45/45 dimensions are also sold as a Scott headset bearing, while equivalent bearings are available under other brands.
Important: Do not substitute this bearing solely because the diameter looks similar. The height and 45°/45° contact angles must also match the frame, fork and headset bearing seats.
When to Replace Your Headset Bearing
A headset bearing may need replacement if you experience:
Rough or notchy steering
Grinding or clicking when turning the bars
Excessive headset play
Stiff or inconsistent steering
Visible corrosion or damaged seals
Replacing the bearing with the correct specification can restore smooth headset operation and precise steering.
Best suited for: bicycle workshops, headset servicing and replacement of compatible 40 x 51.9 x 8mm 45/45 headset bearings.
