Built-up Propeller and spiner. Would be easy to make a mistake aligning spineer, backing plate and blades here. Cut the spiner blade cut-outs by markingthe cut-out profile on the spiner with the supplied template, then drilling two 1/2 inch holes and one 3/4 hole with a step drill where the profile changes direction, then conecting the holes with a Dremel cut-off wheel. Worked out very well. Be carefull drilling the backing plate, it has to be clocked correctly relative to the blades and prop shaft spacer with the propeller mounted on the engine shaft.