Which Ryobi planer do you have? I was having trouble finding
replacement blades for my model AP12 12 inch planer, and found that
the Delta brand Cat 22-562 that I got from Lowe's fit just fine. The
only differences I have observed is that the delta blades have 3 index
holes where the factory blades had 2. All other dimensions are
exactly the same within .001 on my calipers except overall length.
the are 1 MM longer but still fit and turn cleanly

Same machine and you had the same experience I did just this week. A fellow
at HD was glad to let me open the package and stand there and measure the
Delta blades. The Deltas fit fine. I almost had a heart event when I found
out what the aftermarket blades cost.