The first Lighting KE7 had a smooth 9/16 inch prop shaft with shear pin hole. The second Lighting KF7 has same lower unit KG7 5/8 inch with 9 splines and the prop has a built in clutch. If you want to run shear pin prop you need a adapter.
Thats pretty cool! Yes, my KE7 has the smooth shaft with shear pin holes. I have a similar lower that I believe is a Wizard that has a smooth shaft but it doesnt have a hole in the threaded portion like the Merc…So theres yet another size out there?