The "screw base" and "screw head" parts should only be printed if you can't find a proper fitting screw. you need to insert the screw base in the equators, then glue on the screw heads.
screw: 1.5cm M2.5 screw
dimensions: 5.5cm x 5.5cm x 3cm
- center x2
- corner x4
- edge x4
- (only if needed) screw base x1
- (only if needed) screw head x2