Here is a fundamental question that every vinyl lover has asked: why is the hole of a 7-inch single so big?
For the first fifty years of the turntable’s existence, the spindle on which you placed the record was a standard size: approximately .283 inches. That was also the size of the hole drilled into all records.
When Columbia Records introduced the 33 1/3 RPM long-playing album in 1948, they kept the hole in the center the same size. However, Columbia’s archrival, RCA, was most annoyed at this new format. Rather than license Columbia’s technology for their releases, RCA introduced their own new record, the 7-inch single that spun at 45 RPM and had a center hole that measured 1.5 inches in diameter.
Why would they do something like that? Two reasons.
While the LP promised up to 22 minutes of uninterrupted music per side, RCA’s crowed that their 45s could be stacked on the special tall, fat spindle—about 6 inches high—that was exclusive to RCA-manufactured turntables. Once a side of a 45 finished playing after five or six minutes, the tone arm moved away long enough for the next record to drop down onto the platter. The tone arm then swung back into place and the music would continue. With the ability to stack up to ten 45s on the RCA spindle, it was theoretically possible for the music to continue for a full hour without human intervention.
RCA wanted their new format to crush Columbia’s LPs, so they began selling turntables that could only play 45s. The thinking was that once someone bought one of these turntables with the fat spindles, they were theoretically locked into buying music in that format from then on. It was just like the future VHS/Beta and Blu-ray/HD-Video wars.
But there was a more scientific reason for the larger hole. When a new 45 dropped from the spindle onto the turntable, it was required to spin up from a dead stop to 45 RPM very quickly. This torque tended to cause the small holes to go out-of-round very quickly, causing record to wobble as it spun. The larger hole allowed the sudden rotational force to be distributed over a longer path—pi x 1.5 = about 4.712 inches—reducing wear and allowing the hole to stay round longer.
And while we're on the topic, what do you call that plastic piece that snaps into the hole allowing it to be played on a regular turntable spindle? Sorry to disappoint anyone looking for an exotic name. It's simply called a "45 rpm record adapter."