At my wife’s insistence, my hand luggage was larger than I was comfortable with, and it was just small enough for the overhead storage. There’s no doubt in my mind it wouldn’t have dropped into one of the “size checking” frame things they have
The checks I went through were
Security – boarding pass check
X-ray – what it says on the tin
Passport control – just a passport check
Boarding gate – Boarding pass and passport
At no point did anyone question the size/weight of the case I had.
Obviously not a good thing, as it could easily get out of hand