Small-bore
Small-bore refers to calibers with a diameter of or smaller. It may also refer to small-bore rifle competition. The medium-bore refers to calibers with a diameter between up to and large-bore refers to calibers with a diameter of or larger. Miniature bore refers historically to calibers of or smaller.
There is much variance in the use of the term small-bore, which over the years has changed considerably with anything under caliber considered small-bore prior to the mid-19th century.