Over Christmas I noticed the Postal clerk was demonstrating to another customer that her cards were not too thick - over 1/4 inch - by using a cutout that was also cut to the widest an envelope can be without paying extra postage (every penny counts!). I had decided then I would somehow make my own and today I finally got around to it by using a piece of cardboard and carefully cutting an opening to slide my cards through to make sure I won't have to pay that extra 17 cents.
According to the USPS web page, envelopes must fit within these guidelines:
First-Class letter dimensions:
At least 3-1/2 inches high X 5 inches long X .007 inch thick
No more than 6-1/8 inches high X 11-1/2 inches long X 1/4 inch thick
Maximum weight is 3.5 ounces
Letters that are considered nonmachinable are subject to a surcharge.
Length is the dimension parallel to the address.
You may notice that the counter is now gone. It failed and the web site where I got it won't let me have another one because they show I already have one for each of my blogs. Oh, well, it was nice while it lasted.