Screw hole 4mm, connecting 8mm with 2 gaskets

Screw connecting 8mm for engine hole
Height of the screw iunder the head = 25mm
Thread 125
4mm hole with smaller external 7mm recommended specifically for oil cooler.
Screws with 2.5mm holes give a limit the oil flow by doing a pressure in the oil holes => leakage and loss of power consumed by the oil pump