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What would be a good size tube for 1/10 or 1/20 oz gold? Will a penny or dime tube work? Do they sell some sort of spacers, so that the coins aren't rubbing against eachother?

Dime tubes for 1/10
Nickel tubes for 1/4
uncertain about 1/2oz

Swing by an arts-n-crafts store and ask about the little pots used for mixing paints. They are perfect for 1/4 oz and sovereigns.