HERA Arms does not provide the internal diameter of their IRS AR15 Rifle Aluminum Handguards. I'd recommend reaching out to them directly for more information.
HERA Arms does not state what size wrench is needed for the HERA Arms 110504 IRS AR15 Rifle Aluminum Handguard Black Hard Coat Anodized 15". However, from what I could find you will need a 29mm Crowfoot Wrench.