What size beads for a scarf?

I am finally knitting my mom a drop stitch scarf out of Wildfoote (http://www.brownsheep.com/wls.htm - Ragtime, SY300) and I do not know what size beads to buy. I was wondering if any of you knitters out there might know, the sizes are 4, 6, 8, and 10 mm if that helps.

I am making a scarf right now and I am using a size 8 bead. The 6 was to small for the yarn. I am also using sock yarn. Hope this helps.

Thank you! That is what I needed to know, now I need to get to Micheal’s. They have some nice beads right now…