B dim
The B dim chord consists of the B (Perfect unison), D (Minor third) and F (Diminished fifth) notes.

How to play the B dim chord
- Find B (Root) on the piano keyboard
- Add D (Minor third) — 3 semitones above B
- Add F (Diminished fifth) — 6 semitones above B
- Press all 3 notes simultaneously to sound the B dim chord