XJRider.com

Since I had some downtime yesterday, I figured I would investigate the chain on the bike. I seem to have found a mystery seal or gasket. I can't find the part on any of the fiches either. The part has 4br and 161 on it.

https://ibb.co/gmK4zH

https://ibb.co/kW2PzH

Does anyone know what this is? I looked the bike over pretty well and didn't see anything out of order. No fluids leaking, etc.