A 45 rpm adapter (also called a 45 rpm record insert or a "spider") is a small plastic insert that goes in the middle of a 45-rpm record so it will play on a turntable. The adapter pops into place in the center of the record and allows it to fit onto the bottom of the spindle. Once in place, it sits flush with the record, permitting you to leave them on the 45s indefinitely without having to remove and re-insert them each time they are played. Sold in sets of 20.