IHC gas cyl screw

Hi all
All the IHC gas cyl screws I have seen have been marked IHC NHC. On the last rifle
I received The screw is marked IHC O. Is this a rare or uncommon screw? Any info
would be apprciated.
Thanks
Tom

I recently sold one of these, and had second thoughts because I too have only seen the IHC / NHC examples. Then I was told that the IHC / O was the first type (actually there were IHC / O and IHC / o ---note the size of the "O"). They are uncommon, but not really rare according to a couple IHC collectors that I chat with. That all said, if I come across another one I'm going to snag it for my collection. Just my 2 cents.....cheers!
---Brian

Thanks for the info. My O is the same size as the IHC. It is nice to come across
unusual parts.:D
Tom