Lawn-Boy 92-8630 89864 Easy Mulch Cover 21" Lawnboy Side Discharge Block Off
This should also fit the newer duraforce. this part was removed from a older 21" mower from the 1980's. i am not sure of the model number of the mower, but a few are 7229, 7268, 8238, 10525, and probably a few others.