Okay, now I get it....just went and checked my parts bin. The wheel cover overlaps the step on the wheel hub and the step washer prevents them from touching each other. Without that step in the hub you would need a step washer that was way thicker to prevent them from contacting each other. I...
This may help. Link to Parts Tree website drawing showing step washer location.
https://www.partstree.com/models/10515-lawn-boy-gold-series-walk-behind-mower-sn-005900001-005999999-1995/rear-wheel-drive-ass-y-model-no-10515-10520-9/
I will also check my back up wheels I have in storage as I...
Out of the first 7 sites that show up on Google only 2 show as in stock. One won't ship to Canada and the other is $68 US. I bought 2 junk lawnboys for $50 CDN last year. I would be looking for a junker as you can strip them and build up a little parts supply. Especially things like wheels /...
Is that a steel deck? What did you do to prep it? stripper / sanding / ? Not quite sure how to proceed on an aluminum deck.....mines a mess. And do you know where to get replacement decals?