Headset is 1-1/8" threaded.
There might be different stock risers meant for other bikes such as Bike Friday or the Pacific Cycles Reach, or the Airnimal; I had some made from titanium, and before that, used one from Bacchetta, and before that, made my own using 7075 aluminium tubing.
Hi Jur,
The risers shown in the thread about your Ti Swift look nice (along with the bikes). Do you know if they can be bought singly from Titan? And are they significantly lighter than a stock steel one?