Under International Air Transport Association (IATA) Resolution 302, where two airlines on an itinerary differ in their checked baggage allowance, the allowance that applies is determined by the Most Significant Carrier (MSC).
IATA defines the MSC as the carrier performing carriage on the first sector.
If your baggage allowance is 25 kilograms on your first sector, that's the allowance on a connecting flight aboard a different carrier, provided both are IATA members.
Although IATA represents 280 airlines from 120 countries and carries 83 per cent of total air passenger traffic, there are some surprising non-members, primarily among low-cost carriers.
The list includes Ryanair, easyJet, Spirit and Southwest Airlines and, in our own orbit, Jetstar and Tigerair Australia.
Since these airlines do not usually have interline agreements, if you have a connecting flight they will not transfer checked baggage to another airline.
In that case baggage must be retrieved from the first flight and checked in for the connecting flight, with that airline's baggage allowance applying.
If you are travelling aboard different airlines on the same itinerary, hand baggage must comply with the rules set by the airline operating the flight.