Bag measurements

I have a question about bag measurements. I have some Silver Age Ultra Pro bags that are supposed to be 7 1/8" wide (this is what is printed on the packaging.) When I actually measure these though, they are 7 1/4" wide. Is this because the 7 1/8" refers to how wide the interior is?

I have some bags/boards that came with some comics I bought that I really like. They actually measure 7 1/8" wide. I like how snug they fit a standard 7" silver age board and the comic does not have any 'wiggle room' to fall off the board.

I hope I don't sound too OCD with this but I am about to purchase thousands of bags/boards to use on my collection and I would like them to be what I like since it is such a huge investment.

I have been looking at BCW. They too say 7 1/8" on the packaging. I was wondering if anybody here has actually bought these and could physically measure one to let me know if they are really that wide or if it is like the Ultra Pro where they are actually a little wider?

If you know of some other bags that actually measure 7 1/8" across (basically I want them to fit a 7" board very snug.) I would appreciate the direction!

Or if you have any other suggestions about shopping for bags and boards I am all ears. I am however planning to just get poly bags, not mylar. I realize mylar is much safer and longer lasting but it is just not practical for me to spend so much money on them right now. Unless somebody can point out a good deal. For example I have found plenty of options on eBay for 1000 poly bags and boards for between 110 and 150 US dollars. Which is already a big investment for supplies but I would suspect Mylar is quite a bit more expensive. I would consider it if I could get a deal on 1000, but it couldn't be too much more than the poly bags or I wouldn't be able to afford it.

Thanks!