I have taken these measurements
Head Tube Inside Diameter (Top): 42 mm
Head Tube Inside Diameter (Bottom): 42 mm
Fork Steerer Tube (Top): 28.6 mm (1-1/8")
Fork Crown Race Seat (Bottom): 29.8 mm
Depth of the 42 mm diameter: 9.6 mm
You would think it would be a standard is42 headset but there is no chamfer on the inside of the headtube. It is just a flat lip. The headtube is just machined to a bigger diameter for where the bearings are supposed to be.
by Michaeleph
4 Comments
Try this tool: https://www.fsaeasyheadset.com/
Zs42 sounds more likely
In the time it took to make this post you could’ve called or emailed the frame manufacturer and got the only guaranteed correct answer?!
https://www.sheldonbrown.com/headsets.html