Originally Posted by Sam Drucker

If you show the THAI BKK>HKT ticket to the counter agent in SFO at check in, and it is a good connection (same day or next day-next flight out) they should be able to give you a bag tag that shows HKT as the final destination. Then you should be still on the "piece concept" since you are originating in USA. The "piece concept" historically has been two pieces, maximum 70 pounds each. Many USA carriers have cut this limit to 50 pounds each, with a lower charge ($25 on NW) for baggage in the >50 - 70 pound range. The excess baggage charges really escalate above 70 pounds.

THAI has been still observing the 70 pound limit to and from the states; I'm not sure about Cathay Pacific. However, if you get your baggage checked through to destination by the originating carrier, you are "in the system" and safe.

Domestically in Thailand, the LCCs (Low Cost Carriers) like Nok, Thai Air Asia, etc observe some really low limits of 15kg total for checked baggage. If they have interline agreements with Cathay, you should be safe to check through to destination (HKT) and not worry. But THAI is the full service carrier on BKK>HKT and most likely to be successful for you. The LCC's even have a 7kg limit on carry-ons, although the only enforcement I've seen on that is giving you the once-over at checkin (so leave that big heavy carry-on back pack somewhere else when you approach the checkin counter at one of the LCC's)

As a side note, earlier this year when I flew THAI BKK>JFK and NW JFK>MSP (on separate tickets) I was able to show the NW reservation info at THAI checkin at BKK. She generated baggage tags showing BKK>JFK>MSP. I was able to check my bags in BKK (with a max 70 pounds each) and pick them up in JFK (mandatory to go through US customs) then hand them back to THAI (who hands them over to NW) and avoid NW's 50 pound domestic limit. This (by the way) does not appear to be a maneuver that "slipped through the cracks", but rather, the way the system is supposed to work (observing the initial carriers limits through to destination, to or from the USA. It just happens that if I had flown NW all the way to MSP, I would have paid extra if either bag was over 50 pounds.