Banjo Ddim chord (Double C)D diminished on the 5-string banjo: 2 1 2 3, and 3 more shapes

Frets, string 4 to string 1: 2 1 2 3 (first position)

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

Sounds: D A♭ D F  ·  Ddim is D, F, A♭ (1 · ♭3 · ♭5)

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

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 2nd fret it’s 0 5 3 4 (frets counted from the capo), an open Cdim shape. Spike the 5th string at the 7th fret to keep it in tune with the capo.

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