There actually were several other record formats, including a couple of 7-inch ones used some in the US with the small hole. The 45 rpm was the only "small" format that was ever popular in the consumer market, but 16.5 rpm disks, 7" with small hole, saw significant use in studio recordings and in "educational records" used by a number of public schools. (Maybe the educational ones came from the Brits?) I think (dangerous thing, I know) that there was a brief appearance of a 22.5 rpm format that was in the 6 - 8 inch diameter range, with standard(?) small hole; but I saw so few of them that I can't really be sure I remember what they looked like.

Many 50s - 60s era "changers" came with the small spindle for 78s and 33-1/3 rpm records, and had a larger spindle that slipped over that one for the 45s. The "change mechanism" for the small spindle worked/connected inside the larger spindle and actuated a pair of "flippers" to drop one 45 at a time.

"Plugs" that fit into the large hole were also available for purists who used a "real turntable" instead of a changer, and it was surprising to me - at that time - that quite a significant percentage of people who played lots of records insisted that "changers eat your records" and refused to use one. Even then, I'd observed that lots of the small-hole records had chunks eaten out of the hole by being used on changers, but I don't recall ever seeing a 45 (large hole) damaged by a changer.

John