An object with a hole still have collision for the hole

[MrGauHi]

I want to make different parts and assemble them together with the robot arm. So one of my parts have a hole so I can put other parts inside. I tried to import objects created in Solidworks and use an URDF converter add on to convert to URDF file. The feature of the model is fine except for the Collison box where even if I make a bigger hole, there are still collision box on it.
Additionally, I tried to convert the file to obj, or use other building method in solidworks and it still doesn't work. Can someone help me solve this issue?