This is a Rubber Long Barrel Grommet for a 4g wire. These are flexible to help fit around the wire. 

Outer Diameter: 0.85"
Inner Diameter: 0.40"
Height: 0.65"

This grommet DOES FIT most car audio cable.
This grommet DOES NOT FIT my #FAM 4awg ofc cable you will need to go one size larger.