Joined: Feb 2012
Posts: 19,381
Likes: 5,526
From: Rochester, NY
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB
The serrations in the ring bolt hole are artifacts from a female half of the ring bolt and nut which had serrations in it's outer surface to better grip the ring hole. More common on cranks that have the 5th hole positioned behind the crank arm, as it's hard to get a ring nut wrench in there.
The plastic bit looks a lot like a plug for some hole. At about 4mm in diameter (for the "shaft") I suspect it's meant to fit in a M% threaded hole. maybe a bottle cage boss. Anyway I doubt it's intended to be used on the ring, likely just was along for the ride in the packaging. Andy.