Professional Roulette Table I Bought This Roulette Wheel But There's A Problem?

I bought this Roulette wheel but there's a problem? - professional roulette table

I bought this roulette wheel: http://www.americangamingsupply.com/american-style-wooden-professional-roulette-wheel---16-inch.aspx
Here is the problem, the ball sold separately. The website, which I bought for sale bullets roulette wheel, but is available in two sizes, 1 / 2 inch and 3 / 4 inches. What size ball do you think goes with this roulette wheel of the 16-inch?