Mark 1 piercing guide nut

[pops76]

Does it take a special tool to remove the piercing guide nut or what tool is best to unscrew it?  I want to put a new o ring on the piercing pin. Thanks for the help.
Don

[Jonah]

I cut a notch in the middle of an old screwdriver blade to clear the pin but engage the slots on each side.

[TerryM]

  When I replaced the o-rings in mine, I happened to have a screwdriver just the right size.  You might take an oversized screwdriver and grind it so it just fits.  That nut is easily damaged.  Give it a drop of light oil and let it soak in for a day or so, then unscrew it.