This tool reams head tube I.D. to 55.95mm to accept “internal” headset cups with 56.00 - 56.10mm O.D. (1-1/2 ZS standard). Use it with the #690-XXL Facing Cutter and #750 Centering Cone Adaptor. This tool is designed for use with the HTR-1 or HTR-1b Headtube Reamer and Facer.
NOTE: Always use a cutting fluid such as Park Tool CF-2 when machining.
SHIS terminology: The 789 is used for upper and lower head tubes accepting the ZS56 or EC56 headsets.
Manufacturer's Part Number: 789