OK, I'll spill the beans. Turntables, for playing vinyl records, used to have a center post about a quarter of an inch in diameter for 78 or 33 rpm records. Then they came out with 45rpm records with a center hole about an inch in diameter. That thing was a plastic insert for a 45 to let it fit properly on a regular turntable. There was also a solid disk style adapter as well, but the springy one worked better.