Plan 01 port/drill size

[impellerman1]

I have an application that requires a plan 01 arrangement. How do i work out what size my port has to be through the seal chamber cover going from discharge to seal chamber.

 

[flexibox]

1/2"NPT with 1/4 drill through hole.

 

[ACS3]

It is always better to have around 08 mm thru hole.