About the Fdim chord
To play F diminished, use the first shape above. Use your index finger to barre the 1st fret across the G, C, and E strings. Place your middle finger on the 2nd fret of the A string and your pinky finger on the 5th fret of the C string. Strum all four strings and check that each one rings cleanly.
Root
F
Quality
Diminished
Notes
F · Ab · Cb
How the Fdim chord works
F
Root(1)
The home note. It gives the chord its name.
Ab
Minor third(♭3)
The defining minor interval above the root.
Cb
Diminished fifth(♭5)
A lowered fifth that adds harmonic tension.