Cleaver XB Replacement Blade 13 x 17 1317XB Different from most Piranha Blades because it features a semi-cleaver blade shape. This gives it the straight looking, uncupped trailing edge you see. The thickness of the blade is also thinner than Piranha's cupped blade designs. This allows these blades to achieve higher RPM and often a higher top speed. These blades will not work correctly on some brands of outboard motors. Common applications that do not work correctly with these blades are Mercury, Johnson, and Evinrude. If you are not sure if a semi-cleaver blade is appropriate for your use, please contact us for a recommendation.