cluster-ssh: specify terminal font

In my cssh config file, I have: terminal_font=6x13 this default font is too small for me. man cssh says, I can specify other font size with the -f argument, while using "standard X font notation". [Here](https://en.wikipedia.org/wiki/Fixed_(typeface)) is a wikipedia page containing some other fonts types. Unfortunately, none of these work for me: $ cssh host1 host2 -f "7x14" Fatal: Unrecognised font used (7x14). Please amend $HOME/.clusterssh/config with a valid font (see man page). Why does "7x14" not work? How can I use bigger fonts with cssh ?