QualityParts From Oregon That you can depend on. Center hole: 1/2": Requires 3 blades for 61" cut; Requires 2 blades for 41" cut; Superior mulching for bagging and discharge efficiency; Enhanced hardening to keep the blade sharper and more durable; Replaces major brands: Grasshopper, Woods, and Bush Hog; Oregon Equipment Parts 91-539 Blade Grasshopper 21In[400]