I always sent chips abroad as a first class PARCEL, not a first class LETTER, because letters couldn't be more than 1/4" thick.

I always got away with NOT attaching a customs form to SMALL international letters and parcels that contained chips. Lately I am attaching custom forms to letters and parcels that contain chips because you are SUPPOSED to -- not to letters containing papers, but to those containing objects, especially if of dutiable value.

People will be surprised at the cost to send International small first class parcels. I have this in my eBay listings: "(Note: in January 2013, the US post office more than doubled the rate of sending small First Class International Parcels outside of the U.S.! For example, sending a 3-ounce parcel to Canada, went from formerly $3.30 to now $7.35.) "

Robert
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Bernadene Hayes (5th fr left) and Kane Richmond (4th fr left) playing craps in "Don't Gamble With Strangers" (1946).
http://www.antiquegamblingchips.com/StillsC_FemaleStars.htm