which headset for a 2002 cannondale f400 with p-bone headshok

[sow1965]

hello.I have a 2002 cannondale f400 frame and the pbone headshok fork that is correct for that bike.I was wondering which size headset would I buy? Im just confused about sizing.the cups are in the frame and I don't really want to remove them to measure. any advise would be greatly appreciated.thank you

[MendonCycleSmith]

Cannondale Lefty/Headshok Headset SI Cup + Bearing - QHDST/EBO - CannondaleExperts.com

[sow1965]

thank you.