Actual inner diameter of clamp is approx. 30.5mm (when clamp bolt is in line with its counterpart thread), but actual outer diameter of seat tube (in tight close position) is approx. 29.5mm. So the clamp bolt has repetitive bents and finally become broken.
Now I am using handmade 0.3mm shim from shaving gel ballon between seat tube and clamp, and the bolt sits straight!
On my Troll and Karate Monkey I've replaced the SS clamp with the Surly Restrictor clamps to stop the seat post from slipping or damaging the SS clamp. On the Steamroller and LHT the SS clamp seems to work fine.