Banjo Gdim chord (Double C)G diminished on the 5-string banjo: 1 3 1 x, and 3 more shapes

Frets, string 4 to string 1: 1 3 1 x (first position) · 5th string completes it

1. String 4 (C): 1st fret, index finger (barre), D♭
2. String 3 (G): 3rd fret, ring finger, B♭
3. String 2 (C): 1st fret, index finger (barre), D♭
4. String 1 (D): not played
5. String 5, the short g: open, G, in the chord

Sounds: D♭ B♭ D♭  ·  Gdim is G, B♭, D♭ (1 · ♭3 · ♭5)

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

The 5th string: the short g is the root of Gdim, so let it ring.

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