Personally, I would spend the money for an engine manufactur's prop nut and washer set for your engine. The hardware store nuts will fit your crank, but notice that they are not the black hardened and tempered steel that you get from say, OS, or Saito. They are also a much looser fit to the threads. The washers are even worse, A nominal 1/4" is about 0.030" over sized on the IDand the ODand IDmay not be consentric. They were not made for rotating use. They are really soft steel and will deform when you really tighten the nut down, providing you areusing an OEM nut (set for four strokes). Using the hardware store nut, and washer, well the threads may go before you can really tighten down the nut.

When I first started flying 4 strokes, I heard all kinds of storys about them spitting props. Iat first had trouble with a backfire loosening the prop nut set, but I never lost a prop. I finally decided to really tighten the nut and I've not had a problem since with a four stroke. I have spit the prop off a couple 40 size two strokes though and in both cases, it was a hardware store nut coupled wiht a plastic back plate for the spinner. No tapered lock nut to keep things intact if the engine siezes from overheating or backfires.

Most all, if not all four stroke stock sets have amating nut that centers the hardened washer, then has an internal taper on the front to match the taper on the lock nut. Every thing runs true. With a hardware store replacement set of nuts and washers, you probably are introducing more off balance than you would get from most props today if they had never been balanced.

Just my opinion.

Don