MB&F - MB&F Horological Machine No4
MB&F - MB&F Horological Machine No4

MB&F Horological Machine No4


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The aviation-inspired case and engine of the Thunderbolt are one. Neither would, nor could, exist without the other, yet each is so transcendental as to be able to stand alone as a work of art in its own right. The Thunderbolt's engine is the culmination of three long years of development. Each of the 311 components – including the regulator and even the screws – was developed specifically for this anarchistic calibre. Horizontally configured dual mainspring barrels drive two vertical gear trains, transferring power to the twin pods indicating hours/minutes and power reserve.

The sapphire case section and display panels top and bottom allow full access to the flawless fine finishing of HM4's intricate and vibrant micro-mechanics. The sleek aerodynamic form of the Thunderbolt's titanium and sapphire envelope has its roots in Maximilian Büsser's childhood passion for assembling model plane kits. The striking transparent sapphire section of the case requires over 100 hours of machining and polishing to transform an opaque solid block of crystal into a complex, exquisitely curved panel allowing the light to come in and the beauty of Thunderbolt's engine to stand out.

Technical specifications

  • Grade 5 titanium and sapphire
  • 54 mm x 52 mm x 24 mm
  • Three-dimensional manual winding engine
  • Hours, minutes and power reserve indicator
  • Black hand-stitched calfskin

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