You have yours ordered already, but I used one similar to what Frog mentioned. I think it's intent is really for halftones, but works on mesh also. Pretty low cost to have around. I'd figure they can be purchased at a local graphics store, but the sources here that sell them for screen print would be just as good or better.
A pretty good idea I saw the other day, was to spray paint the sides of the mesh to color code. All red are 150, all blue are 160 etc. That doesn't interfere with the mesh frame itself like some other methods do.
I've seen some people use colored Zip lock stripes and those can cause problems sometimes. Others tape them, but they come up or wear down eventually. Spray painting the ends was a good idea.
