We call it "for banjo" but we're quick
to add "also fits most mandolins and bouzoukis." We
might throw in tenor guitar, and a number of other 4-string instruments.
The great majority of banjo fretboards are flat.
Radiused banjo fretboards only came into use within the past 15
years or so, and still account for relatively few instruments.
If you're not sure whether your fretboard is radiused or not,
it probably is flat.
Because of the narrowness of the neck, gauge of
strings, resilience of the capo's rubber material, etc. the radiused
and flat model 5 capos can be used almost
interchangeably on some instruments. If you happen to get your
hands on the wrong one, there's a pretty good chance that it will
work OK, anyway.