Air China and hand baggage allowance

Hi，
How strict are Air China regarding SIZE of hand baggage? Do they use those perspex boxes to ensure your bags are within limits?
I know the weight max is 5KG, and my cabin bag is within the width （40cm) and length (55cm) rules but is about 3cm too deep/thick at one end (wheels stick out). Just worried that I will have to pay extra, to have my hand baggage put in the hold.
I am flying from Hong Kong to Beijing, and then two internal flights later in the month - all via Air China.
Thanks for any help！

Hi,
See details below.  Hope it useful.

Carry-on baggage

The maximum Carry-on baggage allowance for each economy class passenger is 5kg. First class passengers can have 2 pieces of carry on luggage. All other passengers can carry on only one piece. The size may not exceed 20x40x55cm. Carry on baggage in excess of the limit is subject to an excess baggage fee and must be carried as checked baggage.

Check-in Baggage

Adults and children are entitled to a free checked baggage allowance of 40kg, for first class, 30kg, for business class, and 20kg, for economy class while traveling on domestic airlines in China. No free baggage allowance is granted to infants. Groups traveling together are able to combine their baggage allowance if they check in together.

Prohibited Items

The following items are prohibited and cannot be carried in checked or carry on luggage:- Flammable, explosive, corrosive, poisonous, radioactive, polymerizable and magnetized materials. Passengers are forbidden to carry arms, sharp or lethal weapons during flight. Security inspection Passengers and their baggage (including checked and carry on baggage) are subject to the security inspection before boarding the aircraft. N.B. Bottles; including bottle of alcohol purchased at the airport may not be allowed to be carried as cabin luggage.

You should check more information about China Flights & China Airline