What is it / What were they used for?

[Dan in North Houston]

Grandfather was a carpenter, and had a shed full of odds and ends. I've been going through his stuff and have found several things that I cannot identify or figure out what they were used for. I'm going to post on here as I get to them and let the brain trust have a shot.
First post are some small nails, I'd say about 6d, but the head has been flattened and bent 90 degrees. I have a whole handful of them, they are obviously not home-made. Appears to be made for a specific purpose. Any idea what they might have been used for?

 

[Charles in Aus.]

Slate or shingle roofing nails .

 

[jeffcat]

No slate you use copper or stainless nails. Copper is the best and you leave them so the slate can wiggle a little. I have seen these but was a very long time ago. Could be a nail that is machine installed for crates or baskets. Not for hand held nailing. Come to think of it I saw these on and old truck seat somewhere.

 

[CGID]

The shank has barbs near the head. These would have no use for slate shingles. I remember seeing these as a kid. I've never known what they were used for.