piano chord
F♯dim7
F♯1A♭3C♭5E♭♭♭7
Three minor thirds stacked. The seventh is doubly diminished, which is why it is written with a double flat.
Written the other way round it is G♭dim7 — the same twelve keys on a piano, a different piece of notation.
What is true of it
F♯dim7 is F♯, A, C and E♭ — 1, b3, b5 and bb7 counted from F♯.