Root on A string
x-8-9-x-9-10
Fdim7 is the F diminished 7 chord. Its notes are F, A♭, C♭ and E♭♭. Stacked minor thirds. Its symmetrical sound makes it useful as a passing chord.
x-8-9-x-9-10
Numbers show frets from the low E string to the high e string; x means don't play that string.
Every F, A♭, C♭ and E♭♭ on the first 12 frets. The filled dots are the root, F. Build your own shape from any nearby group.
Other F chords
Other diminished 7 chords