This tool reams head tube I.D. to 43.95mm to accept “internal” headset cups with 44.05 - 44.10mm O.D. (1-1/8 ZS standard). It's used with the #690-XL Facing Cutter and #750 Centering Cone.
NOTE: Always use a cutting fluid such as Park Tool CF-2 when machining.
SHIS terminology: The 788 is used for upper or lower headtubes that accept the ZS44 or EC44 headsets.
Manufacturer's Part Number: 788