Here's the application: Large size Salsa Moto Rapido frame. Trying to fit a Carbon Lefty Speed onto it with a Project 321 adapter. The Carbon lefties have fixed clamps, unlike at Al ones, which are adjustable. After all is said & done, there is only 15 mm for the headset to fit with the head tube/adapter with the fixed lefty clamps.

The bottom of the head tube looks like it has about 2 mm clearance before you get into the weld area.

Someone posted a disappeared post about a road Orbit Z headset, which we're checking out - what's the dif between a headset for a road vs mountain?