NV 4500 weird hole?

[Jake92k2500]

Recently got a new to me truck. Checking all the standard mantinance things and I saw a hole I am not sure about. Does anyone know what this is?
1992 Chevy K2500 NV 4500 transmission.
Not familiar with the terminology to describe where it is. I believe it is on the housing that is between the motor and the transmission. It's on the right side. I hope the pictures upload.

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[MIHELA]

That part is called the bellhousing. I believe that hole is for ventilation or drainage. They all have it.