Browning Citori grade 3 20G extractor retaining pin (screw) and extractor ejected into the grass !

[Shotkam]

 Disaster struck when ejecting a cartridge as the complete extractor and empty case ejected into an area of grass. Fortunately I found the extractor but not the tiny threaded retaining pin.

I have bought a replacement Browning / Miroku Ejector Retaining Screw Part No. B1334114 from gunspares which they say fits all Ciroris from .410 up to 12 guage.

My gun is 40 years old and the thread on the new part is different.

Does anyone know the correct thread size and thread pitch so I can order a tap - to tap out the extractor to fit the replacement pin and loctite in.

I know this is a common Browning fault.

Any replies most appreciated.