"I used to have two."

as Grandma said, gazing down "her front" in search of a Hankie.
I doubt they could be made operable, suppose I was that way inclined; I might try, just for fun.
It seems you moved the heel clamp into position and locked in situ by a small screw.
The sole was gripped by moving back to widen or forrard to narrow; yet to work out locking mechanism.
I have used them and curiously managed to skate, after a fashion.
Never well, but I rarely fell. (Almost like a line of poetry that?)

Conversely I can hardly stay upright on wheels; I have NO inclination to try NOW, but have often wondered if I would have been any better on "Skeelers©".
In the unlikely event you know what I mean you are betraying your age.