Smaller one is called a single-jack, and the bigger one is called a double-jack. Single-jack = used by one person.
Double-jack = held by one person, hit by another. My friend and I found a set of single and double-jacks in the gold mining
area in Eastern Oregon......they are in a museum just outside of Baker City, Oregon. Great finds, Lumbercamp. I have been
waiting to read some more of your exploits in the woods. And, am trying to turn some Oregon guys on to hunting some of the lumber camps in Oregon. (I think if I were in the States, and at home, those are some of the places that would see my detector.) Keep us posted on how much iron you are digging out of the ground.