Interesting posting Kevin, it got me thinking about the brushless motors I've used
over the years.
Most mounted behind the nose cone using the tapped holes in the motor body
and a taper lock prop drive onto the motor shaft, others as per your example.
The photos below are of an unbranded 5055 - 720KV motor rated at 765 W with a 6mm dia shaft
which I used in a now deceased model driving a 14 x 7 prop.
The motor body has a shoulder to locate the prop driver which is retained by 4 hex socket hd capscrews.
Much to my surprise there is a significant clearance between shoulder & prop drive counterbore.
With the 4 screws very lightly tightened it was possible to move the prop drive from side to side.
Without a Dial Gauge, I improvised with a digital vernier, and would estimate this movement at about 20 thou.
So even with a shoulder, if fit of the prop driver is not tightly controlled the problem is still there, perhaps on
more expensive motors this is not the case.
Any comments welcome.
Thanks
Colin.