If no one have any data, I'll answer myself to all of you. I remembered that in newest ETZ manual there is technical drawing of ETZ 250 cylinder. I took it to cad and measured the values. They are close to what I took last time with rough angle meter. So I think I'll take 60 degrees as a reference value here and try to make new thread with this angle. You can test it yourself if you want
Regards,
Roman