Guitar chords in the key of C major:
C Dm Em F G Am Bdim

Chord Cdim notes: (Gb), C, Eb and Gb. You must leave out the 6th and 5th strings.

The note Gb on the fourth string is not required, but can be played on the 4th fret if needed.

Cdim - C diminished triad guitar chord's alternative names: C°, C-5, Cm-5, and Cdim. See also: Cdim7 and Cm7b5.

Steps: 1-b3-b5.
1(C), b3(D#/Eb), b5(F#/Gb).