I put a chip in a saf-t-mailer and squish it down a little to make sure that it is under 1/4" thick. I made a cardboard checker which has a 1/4" hole in it to check it. As far as I know the USPS allows you to put the non-machinable tag on any letter size envelope that is not bendable. I do not know of any specification that says what causes it to be not bendable. An envelope that is less than 2 ounces costs $1.47. I also mail everything from my home just to avoid the cage critters at the post office. I still have several hundred dollars in old stamps I get from collections I buy at the estate sales I go to every week. A few weeks ago I got over $200 in stamps for $7. Last week I put a stamp on a package that was 100 years old. BTW - giving the lady who delivers our mail a nice Christmas present every year does not hurt.