Is that an auto-sear pin I see?

Was just browsing gunbroker and came upon this and saw the pin above safety. Is that what I think it is?

http://www.gunbroker.com/Auction/ViewItem.aspx?Item=355527011

Looks like it but if you check the first pic doesnt have the pin all the way through (view from the left) and the later pics do show that pin hole on the right.

I noticed that. I don't get it. Unless it's one of those that has a sear-block. But I cant remember if that's pinned or welded in.

Yup, it's the block.

Here's another one, showing it opened up. Although this one has the pin hole all the way through the reciever.
http://www.gunbroker.com/Auction/ViewItem.aspx?Item=355574049

The pin hole alone is not enough to make it readily convertible if I am not mistaken. The sides where the block is would be to narrow for the m16 parts.

Here's a colt sear block in better light.