The 789 is used in conjunction with the Park Tool HTR-1 Head Tube Reaming and Facing Set to ream head tubes that use the 1.5" internal cup headset standard.

• Sized for 1.5" internal cup headsets
• SHIS: sized for ZS56 and EC56 head tubes
• 55.95 mm outer diameter
• Requires use of the 750.2 Centering Cone Adapter
  

NOTE: Always use cutting fluid such as Park Tool CF-2 when machining.