People who have answered the USPS doesn't know are correct.

I have three close USPS locations. One always charges me, package. The other will drop it through the guide and depending on who, some will pass at 1st class, some will go as non-bendable, not machinable or whatever it's called. Location 4 miles, which is right about middle distance, lady says, put take on the end flap and it passes. (because if it catches on the end flap, it doesn't go through the guide) I haven't tried the 4th little station.

I now own a guide, which the USPS is supposed to have for us, free, and have read the regulations and I still don't know.

I think the problem is, the chips are so close to the 1/4" and then there's a lump, so workers at the counter have to do what they think is best, following the vague guidelines.

I have a favorite rural station, nice lady, always 1st class, in all ways.