Banjo Bdim chord (Open D)B diminished on the 5-string banjo: 3 5 5 3, and 4 more shapes

Frets, string 4 to string 1: 3 5 5 3 (from the 3rd fret)

1. String 4 (D): 3rd fret, index finger (barre), F
2. String 3 (F♯): 5th fret, ring finger, B
3. String 2 (A): 5th fret, little finger, D
4. String 1 (D): 3rd fret, index finger (barre), F
5. String 5, the short f♯: open, F♯, not in the chord

Sounds: F B D F  ·  Bdim is B, D, F (1 · ♭3 · ♭5)

Found in: C major (vii°), G mixolydian (iii°), D dorian (vi°), A minor (ii°)

The 5th string: the short f♯ rubs against the F in this shape, a semitone away: some players let it ring, some skip it.

Open D tuning: f♯DF♯AD, the short 5th string first, then strings 4 to 1.