This is a "Bytcew Wire Wood Fencing Fasteners Staple". Got it on Amazon. It's like a staple except we screw it in. Works great. Better than a staple. Came with a 1.5" screw. Replaced it with a 3" roof screw for attaching to tree.
Gripples work very nicely on the strains. The tool (the contrator torque) is easy to use. We can tweak the tightness with fine control. It's just really nice to work with. However, getting them to loosen with the little pin tool, while they are under strain, might be impossible. So don't use them on the braces.