Your site is wonderful. I was exceedingly happy with my order and the speed at which it was delivered. The marble run I purchased was a big hit with my family. I told them about your company and we will definitely shop with you again!
Size is as-packaged, or the diameter of loose marbles. ("D" is the diameter of round items other than marbles.)
These genuine crystal quartz balls are exactly like the real thing, only smaller! They make dazzling marbles - every one has different reflections and sparkle inside. These are great for collecting too. 18mm is about 23/32".