I have taken some extra pictures and some measurements

seat post is 25 mm I think a 25,2 will fit as well but have not tried.

The outer seat tube diameter is in the middle 29 (could be 28,8 mm as it is including powder-coating) but at the top it has a smaller diameter as it is possible to see on the photo

The Upper Tube is 28,9

Main tube 32,4