Note: 18G jewelry is not standardized - it can be 0.8mm or 0.9mm thread pattern. If a 16G top/post screws into the piece you are testing than it is 0.9mm.
These 10 packs are sold as listed below, (pay attention to threading vs gauge)
18G is 0.8mm thread pattern 16G is 0.9mm thread pattern -Also use this ball for 18G posts that do not fit an 18G top tightly 14G is 1.2mm thread pattern