口径 (kǒu jìng): bore; caliber; diameter; aperture; (fig.) stance (on an issue); version (of events); account; narrative; line

This pistol has a large bore and can load heavier bullets, but its recoil is also stronger.

The engineer measured the actual bore of the water pipe and found it was only eight centimeters, which could not meet the designed flow requirement.

Bullets of different calibers cannot be mixed; otherwise, they may jam or even cause a barrel explosion, which is extremely dangerous.

Astronomers use large-aperture telescopes to observe distant galaxies because the larger the aperture, the more light it collects.

Police found a nine-millimeter shell casing at the scene and preliminarily concluded that the shooter used a standard-issue pistol.