Engineered, manufactured, and inspected to meet the highest standards, Acme Propellers are helping boats discover their true performance potential. The CNC construction process ensures that these propellers are produced with accurate measurements and "dialed in" to enable the development of an optimum propeller for for each make and model of boat. NiBrAl construction. Helps boats reach their true potential NiBrAl material for strength & durability | ACME 4-Blade LH Inboard Propeller, 13-1/2" Diam x 16 Pitch With 1-1/8" Bore