8×59mmRb Breda was an Italian heavy arms cartridge.

The "Rb" in the designation stands for "rebated rim".

8×59mmRB Breda was a caliber created for use by the Royal Italian Army in World War II.

The cartridge was originally designed for use in anti-aircraft heavy machine guns like the Breda M37, Breda M38, and Fiat–Revelli Modello 1935.

It was also used in the experimental Pavesi M42 semi-automatic rifle.