The EF-M barrel width, 60.9mm is bigger than the RF mount, 54mm, so no, I don't see why the lenses would be bigger.
If I'm overlooking something please fill me in.
You clearly don’t grasp the fact that the 54mm EF/RF ‘mount diameter’ is the throat diameter – the inner diameter, not the outer diameter that determines the barrel size at the base of the lens.
Evidently you don't understand what throat diameter means. Let's try an anatomical analogy – if your throat was the same diameter as your neck, you could spew a lot more BS from your head.SwissFrank said:
Likewise you say the RF mount is 54mm and EF-M lenses typically 60mm in diameter? In other words the lenses wouldn't be any bigger at all, would they?
The throat is the inner diameter of the lens mount, not the diameter of the full mount.
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The outer diameter of the EF-M mount is...60.7mm, essentially diameter of all the EF-M lenses (they are all flush with the edge of the thin black ring around the silver mounting surface, which is the place the rubber ring on weather-sealed lenses actually seals on FF cameras). The outer diameter of the RF mount is 69mm, meaning had Canon used the RF mount for M cameras, all the lenses would be 13% larger in diameter, meaning a 28% larger volume assuming the lenses stayed the same length. That's a far cry from 'wouldn't be any bigger at all', isn't it? #factsbeatopinions