This is a craft material, you can obtain them when you have a full set of Dragon Balls and you grab a 8th one, it appears in your inventory as a blank Dragon Ball, which you can't use to summon Shenron.
I had all 7 dragon balls and when i was doing quests i got two of those dragonballs. I tried to put them at Shenrons altar it sayed its not a ball... :D Ill try somthin else if not im selling them :)
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