noun, noun which may take the genitive case particle 'no'
small caliber; small bore
Technical term used for firearms, pipes, and other cylindrical objects to indicate a small internal diameter. Often used attributively with の.
この銃は小口径の弾丸を使う。
This gun uses small-caliber bullets.
小口径のパイプを探している。
I'm looking for a small-bore pipe.