I often tell my classes that not all beads are equal, no matter what the size number is. A Japanese size 11 is about the same size as a Czech size 10. Usually. Unless they aren't. I related how I was struggling with adapting my Czech bead version of the Leaf Tipped Lariat to a Japanese version, and I finally gave up.
Here's a photo of what I'm talking about. The top one is the reject. You can see much more of the core beads (although it's not as aparent in this photo), and see how much bigger those Size 6 beads are in the center of each loop? the lines of the light amethyst don't sit as well because of how big the Size 6 beads are at the core, and last, but not least, the dark amethyst is much darker in the Czech version on the bottom.
But it's not just that. I also have been working on a personal necklace from my Bubbles & Bumps class. (Kit version is on the way - beads to be ordered after I get back from Miami.) I'm doing it in Brown Iris, which is a favorite bead color of mine and as I was working along I realized that I had purchased some Czech one-cuts in Brown Iris not so long ago, and I should be using the one-cuts for extra sparkle. So I started over with the one-cuts. (Side note: I'd actually purchased some from two different vendors - and guess what? They're really different colors. I had to dump them together and mix them to get enough for this project.) And as I'm going along, all of a sudden the spacing on the necklace seemed quite different. I put the original version with Czech size 11s next to the new version with Czech size 11 one-cuts, and the size of those beads is totally different! AGH!! In this case it doesn't matter much. I was easily able to make the changes necessary for it to work, but it's not always that easy.
I'm a little worried about a new class I'll be teaching at Nomadic Notions this summer called Ring Around the Rosie. Making the circles ruffled the way they should look for this project calls for very exact bead sizes to make it work. But I know not everyone will purchase their beads at Nomadic Notions for the class. Some will bring beads in from the outside. And a Toho size 11 is twice the width of a Miyuki size 11. I've decided when I do the kit version, I'm only going to sell it as a kit because if you get the instructions and buy beads that don't work together, not everyone will understand that it's because of the beads and not the designer, ya' know?
A day in the life. Seed bead minutia.