Designation Code Description 1.Diameter  N2 Ø22 mm. Ø25 mm. N3  Ø30 mm. 2.Type  BF Flat Head  BL Protrude Head  BM  Mushroom Head Ø 37  BK  Latch Mushroom Head  BA  Momentary Protrude  BB  Momentary Mushroom Ø 37  BT  Double push button  BCM Mushroom