Because whether it is Leica or Luolai, Hasselblad, each manufacturer's own shutter threads are fine-tuned with the era and batch, that is, for example, the shutter screw of Hasselblad in the 1970s and Hasselblad in the 1980s, the shutter screw of Luolai MX in the 1950s and the shutter screw of Luolai 3.5F in the 1960s, there are subtle differences, because the shutter button is tapered thread, a little difference, it will be a lot worse.
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