BHoles already voided for inserting hemispheres ( a 4 inch drill hole
cutting attachment is used for this ). Hemi's are then test-fitted
before mounting to ensure a correct fit. Note the 'lip' which prevents
them 'falling through' as would be the case witha simple half-sphere.
This 'lip' is invaluable for ensuring solid mounting, and is the same
method employed on the Shawcraft original props in the 1960s.
Also in this picture can be seen one of the two dowel 'keys' which
locate the shoulder section firmly into place ( this being the front 'key')
 once the prop is fully assembled, the second 'key' being at the rear.