saddle

Hello everyone I recently bought a Winchester '94 in 30-30. It was built in 1973 and has the "Antique carbine" look, which means it has some engraving on the receiver and a saddle ring. My question is: how was the saddle ring exactly used? In most pictures it has some kind of leather string...

I got this in a box of goodies. It doesn't fit my Mossberg 835, and I don't have any other shotguns to try it on. I'm not even sure of the brand. I've scoured Google for about an hour trying to find one similar to no avail. Hoping somebody here may recognize it. Thanks in advance for...