When working with Delicas, you can cull your beads before you start your project, OR cull as you go. What do we mean? As precise as Delicas are, you still get some that are a tad longer or shorter than the norm. Depending on the accuracy needed for your project, removing these beads and setting them aside for a less demanding project is Standard Operating Procedure for most beaders. Spill those beads out on a beadmat and start picking out those odd ones with your needle and roll them into a pile away from the rest. Some of us are a bit less fussy, and will cull as we go - look at the bead you are picking up on your needle. Does it match the ones around where it will land in your project? Good? Stitch it in. If not, into the forlorn pile it goes, waiting to become fringe or some other project.
Another thing to be aware of with Delicas: they do not curve into a circular loop well. Why? Because they are cylinder shape. If you need a bead that will "bend" into a curved loop when strung, use a seed bead. Czech seed beads are more donut shaped than their Japanese counterparts, but a tiny 15/0 Japanese seed bead will work fine.