I haven’t ever seen a ridge vent like this one…(which doesn’t make it rare)…anyone?
First time for me, so I have to ask some questions:
Looks like steel, is it stainless?
Is it a home made job, since I see no baffles?
I guess if I was taking sheet metal course I would love to make my own ridge vent too. 
tom
We installed lots of those back in the 70’s but brown. I believe they were aluminum…dented easily…also, when the wind was right they permitted snow/water entry but a better baffle helped that.
Yes it was an aluminum type material…did they always get installed w/ exposed nails?
Thanks
Ah,
I had an alum ridge vent, the nails were covered in roof cement/tar. Just little dabs of it.
However, not the same here, mine where black, had a wind baffle, and were installed in 93.
Just a guess from the photo, were they steel nails, they look rusty. 
tom
Yes, at that time and being dark brown, we just dabbed the nails with a little tar.
I liked it better when the shingle over vents came out.
Yep. That is the way it was. Didn’t work to good in Northern Maine. ha. ha.
Too much snow.
I guess Larry must have come to Maine. Could we say that particular ridge vent design was like the Crescent Wrench. 
Marcel
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they used to make them in mill finish aluminum & brown. 10’ lengths. end caps & connector pieces sold separately. i don’t remember if the nails were exposed or not.
Every time I see these aluminum ridge vents, I normally see leaking and tree debris entering at the ridgeline. I always recommend upgrading to a more improved ridge vent.
Like your first option Dave. Works real well.
Marcel
The question seems to have been answered. This is a case of the industry improving things through negative experience. I also have installed a number of these (in the 80s)
More common for metal roofs? but, it doesn’t have the same ripples that R-panel or standing seam would have.