Improving the appearance would be better, such as adding a ball to the sole of the foot？

You make it like a regular slave strap. I believe they're only made at tailor benches and not at crafting spots.

Cant find it after I download the mod, how to use :) ?

This thing had to be carried in your hands. Attempts to walk with this, led to the fact that the shackles cut into the flesh of the leg, and rubbed it to the meat. It's a really dark thing.

And it adds an element of dark cartoon old-timey humor.