#000 Used for very small insects, generally can be replaced by paper points.
#00 Used for the smallest insects that won't be destroyed by a point. 4~9 mm
#0 Same as #00
#3 The standard pin size. Used for most medium sized insects. 10~100 mm (Different kinds of insects have different anatomies, so use by your own discretion.)
#4 Same as #3.
#7 Used for the largest insects, i.e. Megasoma
#s 1, 2, 5, and 6 generally aren't as important as the ones listed above. A collection will not be lacking if don't use these.