155M Type 1 Howitzer Fiberglass Ring Of Sorts Unknown Help!

I've been cleaning out my father-in-laws estate for several years now and every now and than come across some strange stuff. Just the other day we found this ring of sorts and have no idea what it went and/or goes to. I researched the obvious but came up with all kinds of information which left me at a standstill. With that said, here it is. All ideas and/or information is appreciated. It is make of fiberglass if that helps.

They are called grommets..

They go around the copper driving band of a 155 shell to protect them in transit! They used to be made of platted rope and canvas in days gone by..

Thank you!