The 754.2 is used in conjunction with the Park Tool HTR-1 Head Tube Reaming and Facing Set to ream head tubes that use the 1 1/8" external cup headset standard.
Features
Sized for 1 1/8" external cup headsets
SHIS: sized for EC34 upper and lower head tubes
33.9 mm outer diameter
NOTE: Always use cutting fluid such as Park Tool CF-2 when machining.