Recommended screw sizes for ADDA Fans
Self Tapping

Hole Size (millimeter / inch) Screw Size / Type
2.4 / 0.094 5-20 X length Phillips head Hi Lo STD or Type 25 (thread cutting)
2.8 / 0.110 6-20 X length Phillips head Hi Lo STD or Type 25 (thread cutting)
3.2 / 0.126 8-18 X length Phillips head Hi Lo STD or Type 25 (thread cutting)
3.5 / 0.137 10-16 X length Phillips head Hi Lo STD or Type 25 (thread cutting)
4.2 / 0.165 12-14 X length Phillips head Hi Lo STD or Type 25 (thread cutting)
4.5 / 0.177 12-14 X length Phillips head Hi Lo STD or Type 25 (thread cutting)

Length should be appropriate for your application

See mechanical drawings for hole size in fans