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A 45 RPM adapter (also a 45 RPM record insert, or 45 RPM spindle adapter) is a small plastic or metal insert that fits in the middle of a 45 RPM record player so it can be played on a turntable. The adapter can be a small fixed circle that fits on the bottom of the spindle (meaning only a 45 can be played) or a larger adapter that fits over the entire spindle allowing a stack of 45 seconds to be played. Former RCA Corporation introduced a snap-in plastic insert known as the spider to make 45 RPM records compatible with the smaller spindle size of a 33 in. RPM LP turntable Commissioned by RCA President David Sarnoff and invented by Thomas Hutchison, spiders were common in the 1960s and sold ten million a year.