In addition to the 1/4-inch thickness, the letter rate requires uniform thickness and it must be bendable. I end up paying the parcel rate because I don't want to stick a fellow trader with postage due.

So, I am wondering whether anyone has gotten a "postage due" notice when chips have been sent as letter rate (I haven't).

I like these creative solutions (and photographs) that help generate discussion about cost-effective yet safe ways to mail chips.