Love your Red, White & Blue fabric!!
When you send your blocks out they should measure 12.5". Once the person receives it and puts the block in to their quilt it will measure 12". When you see the blocks at quilterscache that say 12" they will generally end up 12.5 when you are done sewing because that is there unfinished size and you are technically sending unfinished blocks home. The 12 refers to the finished size.
Hope this helps.
Frenchfryqueen please join us. The postage for a small group would probably cost you about $19-$20 for everything from sending your F8 to returning blocks.