This is a specialty hard plastic snap grommet that is just large enough to fit my 1/0 #FAM cable. 

These grommets are very basic to install and help to protect the wire as it goes through holes in your firewall. A must have when installing any power wires through your firewall. These keep the wire from being sliced and shorting out.

Inner Diameter: 0.93"
 
This grommet DOES fit my #FAM branded 1/0 cable due to its oversized insulation.