1/2" bulkhead =   Requires 1 1/8" hole... 12mm hole saw
3/4" bulkhead = Requires 1 1/2" hole...38mm hole saw
1.0" bulkhead =  Requires 1 3/4" hole... 42mm hole saw
1.5" bulkhead = Requires 2 1/2 " hole... 65mm hole saw
2.0" bulkhead =  Requires 3 " hole ...75mm hole saw