Oregon 791-531 Heavy Duty Blades for 61 Grasshopper 320242, 320243, 320245. Replaces Old Oregon 91-531. Blade Width – 2.50. Thickness – 0.250. Blade Length – 21. Center Hole Size – 1/2. Air Lift – 1. The Oregon® 91-531 replacement lawn mower blade is made to the exact OEM specification for optimum performance. Our blades are individually straightened and hardened to provide a consistent, cleaner cut and increase blade longevity. Requires 3 blades for 61″ cut and 2 blades for 41″ cut. High-lift: Aggressive blade angle increases air flow to push debris up and out for superior bagging or side discharge. Major brand replacement: Grasshopper. Fits the Following Models. ATH, ATH600, ATH720, FTH, FTH600, FTH720. Replaces the Following Blades. 320242, 320243, 320244, 320245, 320245B, 320246, 320247, 320322, 70134. 70134, 70134KT, 70142KT, 72517KT.