They are AWG 4 welding cable with some ring terminals connected to the end, with a dab of heat shrink to protect the terminal. Very well done.
My question relates to the sizes of the ring terminals. I ordered a SBL-4-12-5, which means I got a 12 inch cable with a 1/4 (4/16ths) inch terminal on one side, and a 5/16ths inch terminal on the other. The strange thing is that the 5/16ths terminal seems to be a bit small. I'm curious if this is normal, or anything to worry about.
Here you can clearly see the size difference, both ID and OD.
This picture is a bit fuzzy, but shows the 5/16ths inch terminal on top of the 1/4 inch terminal. Notice that the 1/4 inch terminal is larger.
I had to order one more cable to connect my two battery contactors together, and this time I ordered two 1/4 inch terminals, and I will just drill them out.