The inner diameter is only 21mm.
These are intended to be installed onto the engine harness during the build process, The ECU plugs will not fit through the hole.
Fits Most Honda/Acura Firewalls.
1988-2000 Civics, 1990-2001 Acura Integra, 1997-2001 CRV, Honda s2000 AP1 and AP2.