Found what it fits.

[Linked Image]
[Linked Image]

As far as I know, this opening on a low arch catcher model was for mowing up against fences. I've got one with the full cover here! But it fits the bracket on the base perfectly, so maybe there was an option of having the choice of a side throw or catcher.

Or maybe it's off another model that happens to use the same mounting bracket.

Oh yeah, the mower's an old Cortina 2, and I've got the steel catcher that goes with it!