Step 1: Insert a sphere onto the work plane that is 2.5"x2.5".

Step 2: Add a .75" cylinder hole that goes through the center of the sphere. 

Step 3: Add a .75"x.25" box hole off to the side of the central hole to goes through the entirety of the sphere. 

Step 4: Group everything together.

Step 5: Add a box hole that is 3"x3" that will make the brush grip more flush with the work plane and limit support material used. 

Step 6: Group the hole and the brush grip together.

Step 7: Place the brush grip back onto the work plane and export for printing.