Guitar chords in the key of A# or Bb:
Chord Bbdim notes: Bb, Fb, Bb, Db and Fb. (Fb=E).
You should not play the 6th string.
The string 1 (Fb) is left open.
Bb(A#)dim - Bb(A#) diminished triad guitar chord's alternative names: Bb°, Bb-5, Bbm-5, and Bbdim. See also: Bbdim7 and Bbm7b5.
1(A#/Bb), b3(C#/Db), b5(E/Fb).