Banjo Fdim chord (Double C)F diminished on the 5-string banjo: 5 4 5 6, and 2 more shapes

Frets, string 4 to string 1: 5 4 5 6 (from the 4th fret)

1. String 4 (C): 5th fret, middle finger, F
2. String 3 (G): 4th fret, index finger, C♭
3. String 2 (C): 5th fret, ring finger, F
4. String 1 (D): 6th fret, little finger, A♭
5. String 5, the short g: open, G, not in the chord

Sounds: F C♭ F A♭  ·  Fdim is F, A♭, C♭ (1 · ♭3 · ♭5)

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

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

With a capo: on the 5th fret it’s 0 5 3 4 (frets counted from the capo), an open Cdim shape. Spike the 5th string at the 10th fret to keep it in tune with the capo.

Double C tuning: gCGCD, the short 5th string first, then strings 4 to 1.