toro self propelled space/driver

[38racing]

working the unit that sparkplug hit valve. I discovered this part when putting blade adapter back on. it's in bottom of adapter. wondering what the theory of having it stepped on both sides rather than just a thick washer.
https://www.partstree.com/parts/toro-106-3999/

[KE4AVB]

Probably is something to do with clearance needed. Manufactures don't spend more that they have to in making parts.