There are some second declension nouns that end in -ius. (fīlius) son and (socius) ally are nouns that fall in this category. I threw in the vocative and locative for good measure.

This is the singular ending for the Latin word for sword

N : gladius

G : gladi

D : gladio

Ac : gladium

Ab : gladio

L : gladi

V : gladī

The plural endings for the Latin word for sword

N : gladī

G : gladiorum

D : gladīs

Ac : gladios

Ab : gladīs

L : gladīs

V : gladī