Banjo Cdim chord (Open G)C diminished on the 5-string banjo: 4 5 4 4, and 2 more shapes

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

1. String 4 (D): 4th fret, index finger (barre), G♭
2. String 3 (G): 5th fret, middle finger, C
3. String 2 (B): 4th fret, index finger (barre), E♭
4. String 1 (D): 4th fret, index finger (barre), G♭
5. String 5, the short g: open, G, not in the chord

Sounds: G♭ C E♭ G♭  ·  Cdim is C, E♭, G♭ (1 · ♭3 · ♭5)

Found in: D♭ major (vii°), A♭ mixolydian (iii°), E♭ dorian (vi°), B♭ minor (ii°)

The 5th string: the short g rubs against the G♭ in this shape, a semitone away: some players let it ring, some skip it.

Open G tuning: gDGBD, the short 5th string first, then strings 4 to 1.