Park Tool 55.9mm Pilot
The 790 Pilot takes the place of the 789 Reamer for head tube facing with the HTR-1 Headtube Reamer. The 790 is used with the 690-XXL Facing Cutter and #750.2 Centering Cone Adaptor. The tool allows facing head tubes with 55.95 – 55.90mm I.D. (“Internal” 1-1/2” ZS standard).
SHIS terminology: The 790 is used on ZS56 or EC56 upper or lower headtubes.