The snaps on this are giving me major flashbacks, though I can't put my finger on anything specific. My mum was a seamstress and I'm sure I remember finding and playing with something exactly like this in her room as a kid back in the 80s. Will reply here if it comes back to me :) the fact it's adjustable to fixed intervals via the snaps seems too purposeful and practical, though - especially with the metal presumably giving rigidity to whatever it's used for.
Don't think it could be anything for prosthetics, that type of steel would be too liable to cause a patient a wound, we tend to use things like leather or dacron for strapping.
Looks similar to strapping I seen for keeping rolls of sheet metal together.