I'm hardly as much of an expert as Dale or Peter here but my first instinct was also that this is an Ohno school tsuba.
Ohno tsuba tend to be thicker than most other tsuba of similar styles so when you get to the 5mm+ range it is likely an Ohno piece as opposed to Kanayama, Yagyu, etc.
That said however, this would have been a pretty common design and it might be hard to distinguish between Yagyu, Ohno, Myochin or Kanayama with such a design.