I have a Ryobi RY401140 lawn mower. You’d think it would be straightforward—a 21-inch blade should fit, right? But it turns out that not all universal blades are the same. I bought one based on an online recommendation, but it didn’t quite fit. The blade curves upward too close to the center, causing it to sit about 1 mm above the motor’s fan-blade adapter, and the overall width of the blade is a few millimeters greater than the width of the spacer.
I could, of course, just buy an original manufacturer’s blade, but I’d like to upgrade to something better—only I’m not sure how to determine whether a given blade will actually fit or not.